添加travis编译之前执行npm install

Author: hengboy

.travis.yml

@@ -1,8 +1,11 @@
 language: java
 jdk: openjdk8
 node_js: "10"
+before_script:
+  - npm install
 cache:
   directories:
     - $HOME/.m2
     - $HOME/.npm
+    - node_modules
 install: ./mvnw install -DskipTests=true -Dmaven.javadoc.skip=true -Dgpg.skip=true