Fix Grunt memory leak (#906)

Fix the grunt memory leak by isolating the jambo and webpack build into their own process

J=SLAP-1484
TEST=manual

Run "grunt watch" and confirm the build runs when files change

static/Gruntfile.js

@@ -1,5 +1,5 @@
 const webpackConfig = require('./webpack-config');
-const { exec } = require("child_process");
+const { spawnSync } = require('child_process');
 const jamboConfig = require('./jambo.json');
 
 const outputDir = jamboConfig.dirs.output;
@@ -12,34 +12,16 @@ module.exports = function (grunt) {
     watch: {
       all: {
         files: ['**', '!**/node_modules/**', `!${outputDir}/**`],
-        tasks: ['jambobuild', 'webpack',],
-        options: {
-          spawn: false,
-        },
+        tasks: ['build-site']
       },
     },
   });
-
   grunt.loadNpmTasks('grunt-webpack');
   grunt.loadNpmTasks('grunt-contrib-watch');
-
-  grunt.registerTask('jambobuild', 'Jambo build.',
-  function() {
-    // Force task into async mode and grab a handle to the "done" function.
-    var done = this.async();
-    // Run some sync stuff.
-    grunt.log.writeln('Processing task...');
-    // And some async stuff.
-    exec('npx jambo build', (error, stdout, stderr) => {
-      if (error) {
-        console.log(error.message);
-        done(false);
-        return;
-      }
-
-      stderr && console.error(stderr);
-      stdout && console.log(stdout);
-      done();
+  grunt.registerTask('build-site', 'Builds the site.', () => {
+    spawnSync('npx jambo build && npx webpack --config webpack-config.js', {
+      shell: true,
+      stdio: 'inherit'
     });
   });
-}
+}