Restrict gem version

Since our CI is running in a Xenial container with an older version of
Ruby we need to put an upper constraint on the faraday gem.

Signed-off-by: Nicolas Bock <[email protected]>

Author: nicolasbock

Gemfile

@@ -6,3 +6,4 @@ gem "danger-commit_lint"
 gem "danger-mention"
 gem "danger-prose"
 gem "danger-welcome_message"
+gem "faraday", "<1.1.0"