fix(github): head ref name

closes #116

lib/screens/gh_issue.dart

@@ -314,9 +314,7 @@ __typename
     login
   }
   pullRequest {
-    headRef {
-      name
-    }
+    headRefName
   }
 }
 ... on BaseRefForcePushedEvent {
@@ -342,9 +340,7 @@ __typename
     login
   }
   pullRequest {
-    headRef {
-      name
-    }
+    headRefName
   }
   beforeCommit {
     oid

lib/widgets/timeline_item.dart

@@ -358,7 +358,7 @@ class TimelineItem extends StatelessWidget {
           textSpan: TextSpan(children: [
             TextSpan(text: ' restored the '),
             WidgetSpan(
-                child: PrimerBranchName(p['pullRequest']['headRef']['name'])),
+                child: PrimerBranchName(p['pullRequest']['headRefName'])),
             TextSpan(text: ' branch')
           ]),
         );
@@ -370,7 +370,7 @@ class TimelineItem extends StatelessWidget {
             children: [
               TextSpan(text: ' force-pushed the '),
               WidgetSpan(
-                  child: PrimerBranchName(p['pullRequest']['headRef']['name'])),
+                  child: PrimerBranchName(p['pullRequest']['headRefName'])),
               TextSpan(text: ' branch from '),
               TextSpan(
                 text: (p['beforeCommit']['oid'] as String).substring(0, 7),