Fix comment typo by @parroty [fix GH-350]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41785 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/openssl/lib/openssl/digest.rb

@@ -31,7 +31,7 @@ module OpenSSL
     #
     # === Examples
     #
-    #   OpenSSL::Digest.digest("SHA256, "abc")
+    #   OpenSSL::Digest.digest("SHA256", "abc")
     #
     # which is equivalent to:
     #