Upgrade devDependencies and fix newer Webpack warnings

Author: jakezatecky

package.json

@@ -46,7 +46,7 @@
     "gulp": "^3.9.1",
     "gulp-autoprefixer": "^5.0.0",
     "gulp-eslint": "^4.0.0",
-    "gulp-header": "^1.8.8",
+    "gulp-header": "^2.0.5",
     "gulp-mocha": "^5.0.0",
     "gulp-sass": "^3.0.0",
     "gulp-scss-lint": "^0.6.1",
@@ -55,7 +55,7 @@
     "react": "^16.0.0",
     "react-dom": "^16.0.0",
     "react-test-renderer": "^16.0.0",
-    "webpack": "^3.0.0",
+    "webpack": "^4.4.1",
     "webpack-stream": "^4.0.0"
   },
   "dependencies": {

webpack.config.js

@@ -1,4 +1,5 @@
 module.exports = {
+    mode: 'production',
     output: {
         filename: 'index.js',
         libraryTarget: 'umd',

webpack.test.config.js

@@ -1,6 +1,7 @@
 const path = require('path');
 
 module.exports = {
+    mode: 'production',
     output: {
         filename: 'index.js',
         libraryTarget: 'umd',