pantheon.updateScript: support an OAUTH_TOKEN

Sometimes I get rate limited.

pkgs/desktops/pantheon/update.sh

@@ -114,7 +114,26 @@ EOF
     function get_latest_tag ( ) {
         repo_name="$1"
 
-        curl --silent --show-error --fail -X GET "https://api.github.com/repos/elementary/$repo_name/releases/latest" | jq -r '.tag_name'
+        OAUTH_TOKEN=$(printenv OAUTH_TOKEN)
+
+        if [ -n "$OAUTH_TOKEN"  ]; then
+            curl \
+                --silent \
+                --show-error \
+                --fail \
+                -X GET \
+                --header "Authorization: token $OAUTH_TOKEN" \
+                "https://api.github.com/repos/elementary/$repo_name/releases/latest" \
+                | jq -r '.tag_name'
+        else
+            curl \
+                --silent \
+                --show-error \
+                --fail \
+                -X GET \
+                "https://api.github.com/repos/elementary/$repo_name/releases/latest" \
+                | jq -r '.tag_name'
+        fi
     }
 
 #