Fix documentation and add an additional test case for Timezone#=~.

lib/tzinfo/timezone.rb

@@ -1119,12 +1119,14 @@ def hash
       identifier.hash
     end
 
-    # @param regex [Regex] a `Regex` to match against the identifier of this
-    #  {Timezone}.
-    # @return [Integer, nil] `Integer` offset of the match on the identifier,
-    # otherwise `nil` if there is no match.
-    def =~(regex)
-      regex =~ identifier
+    # Matches `regexp` against the {identifier} of this {Timezone}.
+    #
+    # @param regexp [Regexp] a `Regexp` to match against the {identifier} of
+    #   this {Timezone}.
+    # @return [Integer] the position the match starts, or `nil` if there is no
+    #   match.
+    def =~(regexp)
+      regexp =~ identifier
     end
 
     # Returns a serialized representation of this {Timezone}. This method is

test/tc_timezone.rb

@@ -1702,8 +1702,13 @@ def test_hash
 
   define_method("test_=~_operator_matches_against_identifier") do
     tz = TestTimezone.new('Europe/London')
-    assert_equal(0, tz  =~ /Europe\/London/)
-    assert_nil(tz =~ /America\/NewYork/)
+    assert_equal(0, tz  =~ /\AEurope\/London\z/)
+    assert_equal(6, tz  =~ /\/London/)
+  end
+
+  define_method("test_=~_operator_returns_nil_when_regexp_does_not_match") do
+    tz = TestTimezone.new('Europe/London')
+    assert_nil(tz  =~ /America\/New_York/)
   end
 
   def test_marshal_data