Use retriable 1.x

Retriable version 2.0.0.beta is now released and its API changed.
Google-api-client does not work with the new API.
As a quick fix, specify retriable version in '>= 1.4 < 2.0'

tasks/gem.rake

@@ -31,7 +31,7 @@ namespace :gem do
     s.add_runtime_dependency('multi_json', '>= 1.0.0')
     s.add_runtime_dependency('extlib', '>= 0.9.15')
     s.add_runtime_dependency('jwt', '>= 0.1.5')
-    s.add_runtime_dependency('retriable', '>= 1.4')
+    s.add_runtime_dependency('retriable', '~> 1.4')
     # Dependencies used in the CLI
     s.add_runtime_dependency('launchy', '>= 2.1.1')