Fix milestone API specs in Ruby 2.1

Ruby 2.3:
```
URI.parse('http://foo/bar?baz quux')
=> #<URI::HTTP http://foo/bar?baz%20quux>
```

Ruby 2.1:
```
URI.parse('http://foo/bar?baz quux')
URI::InvalidURIError: bad URI(is not URI?): http://foo/bar?baz quux
```

.gitlab-ci.yml

@@ -166,11 +166,6 @@ spinach 9 10: *spinach-knapsack
 .ruby-21: &ruby-21
   image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.1-git-2.7-phantomjs-2.1"
   <<: *use-db
-  only:
-    - master@gitlab-org/gitlab-ce
-    - master@gitlab-org/gitlab-ee
-    - master@gitlab/gitlabhq
-    - master@gitlab/gitlab-ee
   cache:
     key: "ruby21"
     paths:

spec/support/api_helpers.rb

@@ -18,7 +18,7 @@ module ApiHelpers
   #
   # Returns the relative path to the requested API resource
   def api(path, user = nil)
-    "/api/#{API::API.version}#{path}" +
+    "/api/#{API::API.version}#{URI.escape(path)}" +
       # Normalize query string
       (path.index('?') ? '' : '?') +