chore(dependency): Update supported Node version

The updated version of micromatch requires node 8 or later.

Author: gingerchris

.travis.yml

@@ -7,4 +7,4 @@ before_script:
   - yarn install
   - yarn run build
 node_js:
-  - "7"
+  - "8"

README.md

@@ -86,7 +86,7 @@ After that, you will be able to build TypeScript files with webpack.
 
 ## NodeJS versions
 
-**The loader supports NodeJS 4 and newer.**
+**The loader supports NodeJS 8 and newer.**
 
 ## tsconfig.json