Eslint fixes for v4x (#989)

* UPDATE .eslintrc

* UPDATE lint task

* FIX lint errors

* CLEANUP

* FIX no-eq-null warning

* FIX many jsdoc warnings

* FIX jsdoc issues

* FIX jsdoc warnings

* FIX jsdoc

* FIX eqeq and no-eq-null

* ADD lint to travis

* UPDATE test env for eslint

packages/docsify-server-renderer/index.js

@@ -21,6 +21,7 @@ function mainTpl(config) {
   if (config.repo) {
     html += tpl.corner(config.repo)
   }
+
   if (config.coverpage) {
     html += tpl.cover()
   }
@@ -154,12 +155,14 @@ export default class Renderer {
         if (!res.ok) {
           throw Error()
         }
+
         content = await res.text()
         this.lock = 0
       } else {
         content = await readFileSync(filePath, 'utf8')
         this.lock = 0
       }
+
       return content
     } catch (e) {
       this.lock = this.lock || 0