Make spec description for MatchData IndexError more readable

Author: rwstauner

spec/ruby/core/matchdata/begin_spec.rb

@@ -37,7 +37,7 @@
       match_data.begin(obj).should == 2
     end
 
-    it "raises IndexError if index is out of matches" do
+    it "raises IndexError if index is out of bounds" do
       match_data = /(?<f>foo)(?<b>bar)/.match("foobar")
 
       -> {

spec/ruby/core/matchdata/byteoffset_spec.rb

@@ -72,7 +72,7 @@ def obj.to_int; 2; end
       }.should raise_error(IndexError, "undefined group name reference: y")
     end
 
-    it "raises IndexError if index is out of matches" do
+    it "raises IndexError if index is out of bounds" do
       m = /(?<f>foo)(?<b>bar)/.match("foobar")
 
       -> {