Mock man:build task on jruby

So that `rake install:local` at least works.

Rakefile

@@ -199,68 +199,72 @@ task :rubocop do
 end
 
 namespace :man do
-  ronn_dep = development_dependencies.find do |dep|
-    dep.name == "ronn"
-  end
-
-  ronn_requirement = ronn_dep.requirement.to_s
+  if RUBY_ENGINE == "jruby"
+    task(:build) {}
+  else
+    ronn_dep = development_dependencies.find do |dep|
+      dep.name == "ronn"
+    end
 
-  begin
-    gem "ronn", ronn_requirement
+    ronn_requirement = ronn_dep.requirement.to_s
 
-    require "ronn"
-  rescue LoadError
-    task(:build) { abort "We couln't activate ronn (#{ronn_requirement}). Try `gem install ronn:'#{ronn_requirement}'` to be able to build the help pages" }
-  else
-    directory "man"
+    begin
+      gem "ronn", ronn_requirement
 
-    index = []
-    sources = Dir["man/*.ronn"].map {|f| File.basename(f, ".ronn") }
-    sources.map do |basename|
-      ronn = "man/#{basename}.ronn"
-      manual_section = ".1" unless basename =~ /\.(\d+)\Z/
-      roff = "man/#{basename}#{manual_section}"
+      require "ronn"
+    rescue LoadError
+      task(:build) { abort "We couln't activate ronn (#{ronn_requirement}). Try `gem install ronn:'#{ronn_requirement}'` to be able to build the help pages" }
+    else
+      directory "man"
 
-      index << [ronn, File.basename(roff)]
+      index = []
+      sources = Dir["man/*.ronn"].map {|f| File.basename(f, ".ronn") }
+      sources.map do |basename|
+        ronn = "man/#{basename}.ronn"
+        manual_section = ".1" unless basename =~ /\.(\d+)\Z/
+        roff = "man/#{basename}#{manual_section}"
 
-      file roff => ["man", ronn] do
-        sh "#{Gem.ruby} -S ronn --roff --pipe #{ronn} > #{roff}"
-      end
+        index << [ronn, File.basename(roff)]
 
-      file "#{roff}.txt" => roff do
-        sh "groff -Wall -mtty-char -mandoc -Tascii #{roff} | col -b > #{roff}.txt"
-      end
+        file roff => ["man", ronn] do
+          sh "#{Gem.ruby} -S ronn --roff --pipe #{ronn} > #{roff}"
+        end
 
-      task :build_all_pages => "#{roff}.txt"
-    end
+        file "#{roff}.txt" => roff do
+          sh "groff -Wall -mtty-char -mandoc -Tascii #{roff} | col -b > #{roff}.txt"
+        end
 
-    file "index.txt" do
-      index.map! do |(ronn, roff)|
-        [File.read(ronn).split(" ").first, roff]
+        task :build_all_pages => "#{roff}.txt"
       end
-      index = index.sort_by(&:first)
-      justification = index.map {|(n, _f)| n.length }.max + 4
-      File.open("man/index.txt", "w") do |f|
-        index.each do |name, filename|
-          f << name.ljust(justification) << filename << "\n"
+
+      file "index.txt" do
+        index.map! do |(ronn, roff)|
+          [File.read(ronn).split(" ").first, roff]
+        end
+        index = index.sort_by(&:first)
+        justification = index.map {|(n, _f)| n.length }.max + 4
+        File.open("man/index.txt", "w") do |f|
+          index.each do |name, filename|
+            f << name.ljust(justification) << filename << "\n"
+          end
         end
       end
-    end
-    task :build_all_pages => "index.txt"
+      task :build_all_pages => "index.txt"
 
-    task :clean do
-      leftovers = Dir["man/*"].reject do |f|
-        File.extname(f) == ".ronn"
+      task :clean do
+        leftovers = Dir["man/*"].reject do |f|
+          File.extname(f) == ".ronn"
+        end
+        rm leftovers if leftovers.any?
       end
-      rm leftovers if leftovers.any?
-    end
 
-    desc "Build the man pages"
-    task :build => ["man:clean", "man:build_all_pages"]
+      desc "Build the man pages"
+      task :build => ["man:clean", "man:build_all_pages"]
 
-    desc "Remove all built man pages"
-    task :clobber do
-      rm_rf "lib/bundler/man"
+      desc "Remove all built man pages"
+      task :clobber do
+        rm_rf "lib/bundler/man"
+      end
     end
   end
 end