feat(deps): Remove core-js dependency. (#3379)

The core-js was used for dom-serialize, used to support a single function
in stringify (serialize) for a single rare browser, IE8, in logs sent back to
the server. By dropping this dependency we reduce the size of karma with
minimal impact on use cases.

Author: johnjbarton

client/main.js

@@ -1,7 +1,6 @@
 /* global io */
 /* eslint-disable no-new */
 
-require('core-js/stable')
 varKarma=require('./karma')
 varStatusUpdater=require('./updater')
 varutil=require('../common/util')

common/stringify.js

@@ -1,4 +1,10 @@
-varserialize=require('dom-serialize')
+varserialize=null
+try{
+serialize=require('dom-serialize')
+}catch(e){
+// Ignore failure on IE8
+}
+
 varinstanceOf=require('./util').instanceOf
 
 functionisNode(obj){
@@ -56,7 +62,11 @@ function stringify (obj, depth) {
 }elseif(obj.outerHTML){
 returnobj.outerHTML
 }elseif(isNode(obj)){
-returnserialize(obj)
+if(serialize){
+returnserialize(obj)
+}else{
+return'Skipping stringify, no support for dom-serialize'
+}
 }elseif(instanceOf(obj,'Error')){
 returnobj.toString()+'\n'+obj.stack
 }else{