lib/csv.rb: [DOC] Fix typo [ci skip][Fix GH-907]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50709 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/csv.rb

@@ -517,7 +517,7 @@ class CSV
     end
 
     #
-    # Collapses the row into a simple Hash.  Be warning that this discards field
+    # Collapses the row into a simple Hash.  Be warned that this discards field
     # order and clobbers duplicate fields.
     #
     def to_hash