add VM type

src/execution-context.js

@@ -95,6 +95,9 @@ function ExecutionContext () {
   }
 
   this.detectNetwork = function (callback) {
+    if (this.isVM()) {
+      callback(null, { id: '-', name: 'VM' })
+    } else {
       this.web3().version.getNetwork((err, id) => {
         var name = null
         if (err) name = 'Unknown'
@@ -104,10 +107,11 @@ function ExecutionContext () {
         else if (id === '3') name = 'Ropsten'
         else if (id === '4') name = 'Rinkeby'
         else if (id === '42') name = 'Kovan'
-      else name = 'Unknown'
+        else name = 'Custom'
         callback(err, { id, name })
       })
     }
+  }
 
   this.internalWeb3 = function () {
     return web3