upgrade(docker): use node v8 by default

Dockerfile

@@ -7,7 +7,7 @@
 # Docker image for Alpine Linux with latest ShellCheck, a static analysis tool for shell scripts.
 # https://hub.docker.com/r/nlknguyen/alpine-shellcheck/
 # FROM nlknguyen/alpine-shellcheck
-FROM mhart/alpine-node:7
+FROM mhart/alpine-node:8
 MAINTAINER Huan LI <zixia@zixia.net>
 
 RUN  apk update && apk upgrade \

package-lock.json

 {
   "name": "wechaty",
-  "version": "0.8.94",
+  "version": "0.8.95",
   "lockfileVersion": 1,
   "dependencies": {
     "@ava/babel-preset-stage-4": {
@@ -6113,12 +6113,6 @@
       "integrity": "sha1-aw6DdgA9evGGT434+J3QBZ/80DI=",
       "dev": true
     },
-    "tslib": {
-      "version": "1.7.1",
-      "resolved": "https://registry.npmjs.org/tslib/-/tslib-1.7.1.tgz",
-      "integrity": "sha1-vIAEFkaRkjp5/oN4u+s9ogF1OOw=",
-      "dev": true
-    },
     "tslint": {
       "version": "5.3.2",
       "resolved": "https://registry.npmjs.org/tslint/-/tslint-5.3.2.tgz",
@@ -6159,12 +6153,6 @@
         }
       }
     },
-    "tsutils": {
-      "version": "2.3.0",
-      "resolved": "https://registry.npmjs.org/tsutils/-/tsutils-2.3.0.tgz",
-      "integrity": "sha1-luZh18I2PzGtyJkqxnu+e3/BdeU=",
-      "dev": true
-    },
     "tuling123-client": {
       "version": "0.0.1",
       "resolved": "https://registry.npmjs.org/tuling123-client/-/tuling123-client-0.0.1.tgz",