Add contributors plugin (#126)

source/plugins/contributors/queries/commit.graphql

@@ -0,0 +1,12 @@
+query ContributorsCommit {
+  repository(owner: "$owner" name: "$repo") {
+    object(expression: "$expression") {
+      ... on Commit {
+        oid
+        abbreviatedOid
+        messageHeadline
+        committedDate
+      }
+    }
+  }
+}