check navigator in node env

remix-solidity/src/compiler/compiler.js

@@ -73,7 +73,7 @@ function Compiler (handleImportCall) {
   function onInternalCompilerLoaded () {
     if (worker === null) {
       var compiler
-      var userAgent = navigator && navigator.userAgent ? navigator.userAgent.toLowerCase() : "-"
+      var userAgent = (typeof (navigator) != 'undefined') && navigator.userAgent ? navigator.userAgent.toLowerCase() : "-"
       if (typeof (window) === 'undefined' || userAgent.indexOf(' electron/') > -1) {
         compiler = require('solc')
       } else {