Add support for file comments in PRs (#1717)

* Add specs for file PR comments

* Add support for file comments in PRs

Author: camillof

lib/octokit/client/pull_requests.rb

@@ -197,22 +197,30 @@ def pull_request_comment(repo, comment_id, options = {})
       # @param body [String] Comment content
       # @param commit_id [String] Sha of the commit to comment on.
       # @param path [String] Relative path of the file to comment on.
-      # @param line [Integer] Line index in the diff to comment on.
+      # @param line [Integer] Optional line index in the diff to comment on.
       #                       For a multi-line comment, the last line of the range
       #                       and specify 'start_line' in the 'options'.
+      #                       If not specified, the comment will be on the whole file.
       # @return [Sawyer::Resource] Hash representing the new comment
       # @deprecated The position will be deprecated in the next major version. Please refer to the details below.
       # @see https://developer.github.com/v3/pulls/comments/#create-a-comment
       # @example
       #   @client.create_pull_request_comment("octokit/octokit.rb", 163, ":shipit:",
       #     "2d3201e4440903d8b04a5487842053ca4883e5f0", "lib/octokit/request.rb", 47)
-      def create_pull_request_comment(repo, pull_id, body, commit_id, path, line, options = {})
-        options.merge!({
-                         body: body,
-                         commit_id: commit_id,
-                         path: path,
-                         line: line
-                       })
+      def create_pull_request_comment(repo, pull_id, body, commit_id, path, line = nil, options = {})
+        comment = {
+          body: body,
+          commit_id: commit_id,
+          path: path
+        }
+
+        if line.nil?
+          comment[:subject_type] = 'file'
+        else
+          comment[:line] = line
+        end
+
+        options.merge! comment
         post "#{Repository.path repo}/pulls/#{pull_id}/comments", options
       end
       alias create_pull_comment create_pull_request_comment