Update gem locations in Gemfile.

Author: gkellogg

Gemfile

@@ -10,7 +10,7 @@ group :develop do
   gem "rdf-vocab",      git: "https://github.com/ruby-rdf/rdf-vocab",       branch: "develop"
   gem "rdf-xsd",        git: "https://github.com/ruby-rdf/rdf-xsd",         branch: "develop"
 
-  gem "ebnf",           git: "https://github.com/gkellogg/ebnf",            branch: "develop"
+  gem "ebnf",           git: "https://github.com/dryruby/ebnf",             branch: "develop"
   gem "sxp",            git: "https://github.com/dryruby/sxp",              branch: "develop"
 
   gem 'rest-client-components'