removing support for node 7

See webpack-contrib/mini-css-extract-plugin#203

Author: weaverryan

.travis.yml

@@ -9,8 +9,14 @@ cache:
 matrix:
   include:
     - os: linux
-      node_js: "7"
+      node_js: "10"
       env: JOB_PART=travis:lint
+    - os: linux
+      node_js: "10"
+      env: JOB_PART=test
+    - os: linux
+      node_js: "9"
+      env: JOB_PART=test
     - os: linux
       node_js: "8"
       env: JOB_PART=test

CHANGELOG.md

@@ -29,6 +29,10 @@
 See the [browserslist](https://github.com/browserslist/browserslist) library
 for a full description of all of the valid browser descriptions.
 
+ * Node 7 is no longer supported. This is because the new
+   `mini-css-extract-plugin` does not support it (and neither)
+   does Yarn.
+
  * Introduced a new `configureSplitChunks()` method that can be
    used to further configure the `optimizations.splitChunks` configuration.