Fix require failure in browser code due to proxy library

Gulpfile.js

@@ -26,6 +26,9 @@ function webpackConfig(extension, overrides) {
         test: /\.js$/,
         exclude: /node_modules/,
         loader: 'babel-loader?optional=runtime'
+      }, {
+        test: /\.json/,
+        loader: 'json-loader'
       }]
     }
   };

package.json

@@ -48,6 +48,7 @@
     "gulp-rename": "~1.2.0",
     "gulp-uglify": "~1.1.0",
     "istanbul": "~0.3.5",
+    "json-loader": "^0.5.2",
     "mocha": "~2.1.0",
     "webpack": "~1.5.3",
     "yargs": "~1.3.1"

src/core/server.js

@@ -4,7 +4,6 @@ const _ = require('lodash');
 const assert = require('assert');
 const util = require('util');
 const url = require('url');
-const HttpsProxyAgent = require('https-proxy-agent');
 const LRU = require('lru-cache');
 const EventEmitter = require('events').EventEmitter;
 const RippleError = require('./rippleerror').RippleError;
@@ -447,6 +446,12 @@ Server.prototype.connect = function() {
     const parsed = url.parse(this._opts.url);
     const opts = url.parse(this._remote.proxy);
     opts.secureEndpoint = parsed.protocol === 'wss:';
+    let HttpsProxyAgent;
+    try {
+      HttpsProxyAgent = require('https-proxy-agent');
+    } catch (error) {
+      throw new Error('"proxy" option is not supported in the browser');
+    }
     const agent = new HttpsProxyAgent(opts);
 
     this._ws = new WebSocket(this._opts.url, {agent: agent});