* doc/syntax/control_expressions.rdoc: fix a missing "a"

[fix GH-888][ci skip] Patch by @riffraff

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50442 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Fri May  8 15:05:57 2015  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
+
+	* doc/syntax/control_expressions.rdoc: fix a missing "a"
+	  [fix GH-888][ci skip] Patch by @riffraff
+
 Fri May  8 12:11:33 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* vm_eval.c (rb_method_call_status): resolve refined method entry

doc/syntax/control_expressions.rdoc

@@ -441,7 +441,7 @@ for proper usage of +retry+.
 
 == Flip-Flop
 
-The flip-flop is rarely seen conditional expression.  It's primary use is
+The flip-flop is a rarely seen conditional expression.  It's primary use is
 for processing text from ruby one-line programs used with <code>ruby -n</code>
 or <code>ruby -p</code>.