chore: update travis (#16)

Author: atian25

.travis.yml

@@ -3,11 +3,15 @@ language: node_js
 node_js:
   - '6'
   - '8'
+  - '10'
+  - '12'
+before_install:
+  - npm i npminstall -g
 install:
-  - npm i npminstall && npminstall
+  - npminstall
 script:
   - npm run ci
 after_script:
   - npminstall codecov && codecov
-services:
+services:	
   - mysql