CI add test stage with node 7.x

.gitlab-ci.yml

@@ -593,6 +593,19 @@ js-test:
   tags:
     - rust
     - rust-stable
+js-test-node_7:
+  stage: test
+  image: parity/rust-debian-node_7:gitlab-ci
+  before_script:
+    - git submodule update --init --recursive
+    - export JS_FILES_MODIFIED=$(git --no-pager diff --name-only $CI_BUILD_REF^ $CI_BUILD_REF | grep ^js/ | wc -l)
+    - if [ $JS_FILES_MODIFIED -eq 0 ]; then echo "Skipping JS deps install since no JS files modified."; else ./js/scripts/install-deps.sh;fi
+  script:
+    - if [ $JS_FILES_MODIFIED -eq 0 ]; then echo "Skipping JS lint since no JS files modified."; else ./js/scripts/lint.sh && ./js/scripts/test.sh && ./js/scripts/build.sh; fi
+  tags:
+    - rust
+    - rust-stable
+  allow_failure: true
 test-rust-beta:
   stage: test
   only: