Display all syntax error messages when catching SyntaxException

Previously when catching syntax errors in the REPL, we were only showing
the last syntax error displayed by the ruby output. However, ruby can
generate multiple syntax error messages within a single SyntaxException.
For example, this code generates multiple syntax error messages:
```
$ ruby -e 'puts {"key"=>"val"}.to_json'
-e:1: syntax error, unexpected =>, expecting '}'
puts {"key"=>"val"}.to_json
-e:1: syntax error, unexpected '}', expecting end-of-input
puts {"key"=>"val"}.to_json
```
We can't predict which error message would be most helpful for the
consumer - we should show both of them.

This commit modifies the string replacement we're doing when printing
SyntaxExceptions so any number of syntax error lines will be shown
correctly.

Issue: #2102
The error message of SyntaxError is different from Ruby's one

lib/pry/pry_instance.rb

@@ -627,7 +627,7 @@ def handle_line(line, options)
     begin
       complete_expr = Pry::Code.complete_expression?(@eval_string)
     rescue SyntaxError => e
-      output.puts "SyntaxError: #{e.message.sub(/.*syntax error, */m, '')}"
+      output.puts e.message.gsub(/^.*syntax error, */, "SyntaxError: ")
       reset_eval_string
     end
 

spec/syntax_checking_spec.rb

@@ -23,24 +23,42 @@
     end
   end
 
-  ([
+  [
     ["end"],
     ["puts )("],
     ["1 1"],
-    ["puts :"]
-  ] + [
+    ["puts :"],
+
     # in this case the syntax error is "expecting ')'".
     ["def", "method(1"],
+
     # in this case the syntax error is "expecting keyword_end".
-    ["o = Object.new.tap{ def o.render;", "'MEH'", "}"]
-  ]).compact.each do |foo|
+    ["o = Object.new.tap{ def o.render;", "'MEH'", "}"],
+
+    # multiple syntax errors reported in one SyntaxException
+    ["puts {'key'=>'val'}.to_json"]
+  ].compact.each do |foo|
     it "should raise an error on invalid syntax like #{foo.inspect}" do
       redirect_pry_io(InputTester.new(*foo), @str_output) do
         Pry.start
       end
 
       expect(@str_output.string).to match(/SyntaxError/)
     end
+
+    it "should display the correct number of errors on invalid syntax like #{foo.inspect}" do
+      begin
+        # rubocop:disable Security/Eval
+        eval(foo.join("\n"))
+        # rubocop:enable Security/Eval
+      rescue SyntaxError => e
+        error_count = e.message.scan(/syntax error/).count
+      end
+      expect(error_count).not_to be_nil
+
+      pry_output = mock_pry(*foo)
+      expect(pry_output.scan(/SyntaxError/).count).to eq(error_count)
+    end
   end
 
   it "should not intefere with syntax errors explicitly raised" do