Fix grammar 'an hyphen' -> 'a hyphen' [ci skip]

actionview/lib/action_view/helpers/number_helper.rb

@@ -92,7 +92,7 @@ def number_to_phone(number, options = {})
       #   (defaults to "%u%n").  Fields are <tt>%u</tt> for the
       #   currency, and <tt>%n</tt> for the number.
       # * <tt>:negative_format</tt> - Sets the format for negative
-      #   numbers (defaults to prepending an hyphen to the formatted
+      #   numbers (defaults to prepending a hyphen to the formatted
       #   number given by <tt>:format</tt>).  Accepts the same fields
       #   than <tt>:format</tt>, except <tt>%n</tt> is here the
       #   absolute value of the number.

activesupport/lib/active_support/number_helper.rb

@@ -78,7 +78,7 @@ def number_to_phone(number, options = {})
     #   (defaults to "%u%n").  Fields are <tt>%u</tt> for the
     #   currency, and <tt>%n</tt> for the number.
     # * <tt>:negative_format</tt> - Sets the format for negative
-    #   numbers (defaults to prepending an hyphen to the formatted
+    #   numbers (defaults to prepending a hyphen to the formatted
     #   number given by <tt>:format</tt>).  Accepts the same fields
     #   than <tt>:format</tt>, except <tt>%n</tt> is here the
     #   absolute value of the number.