fix(compiler): reject promise with real error

When the webpack compiler fails, the error is not used in the rejection, so the promise is always rejected with `undefined`.
Fix this by respecting the error. Construct real error object as well.

Author: rosen-vladimirov

lib/compiler.js

@@ -25,13 +25,13 @@ exports.runWebpackCompiler = function runWebpackCompiler(config, $mobileHelper,
                 }
                 resolveBase();
             }
-            function reject() {
+            function reject(error) {
                 if (isResolved) return;
                 isResolved = true;
                 if (childProcess) {
                     childProcess.removeListener("message", resolveOnWebpackCompilationComplete);
                 }
-                rejectBase();
+                rejectBase(error);
             }
 
             console.log(`Running webpack for ${config.platform}...`);
@@ -93,10 +93,9 @@ exports.runWebpackCompiler = function runWebpackCompiler(config, $mobileHelper,
                 if (code === 0) {
                     resolve();
                 } else {
-                    reject({
-                        code,
-                        message: `child process exited with code ${code}`,
-                    });
+                    const error = new Error(`Executing webpack failed with exit code ${code}.`);
+                    error.code = code;
+                    reject(error);
                 }
             });
         });