remove 1.9 build because 1.9-dev is gone

.travis.yml

@@ -5,6 +5,3 @@ rvm:
 branches:
   only:
     - master
-env:
-  - ""
-  - "GRAPHQL_19=true"

Gemfile

@@ -1,8 +1,3 @@
 source 'https://rubygems.org'
 
 gemspec
-if ENV["GRAPHQL_19"]
-  puts "1.9-dev compatibility mode"
-  gem "graphql", github: "rmosolgo/graphql-ruby", branch: "1.9-dev"
-  gem "graphql-client", github: "github/graphql-client", branch: "support-1.9-dev"
-end