Fix extract-text-webpack-plugin dependency

Author: alexdevero

package.json

@@ -50,7 +50,7 @@
     "css-loader": "^0.28.10",
     "electron": "^1.8.3",
     "electron-packager": "^11.1.0",
-    "extract-text-webpack-plugin": "^3.0.2",
+    "extract-text-webpack-plugin": "^4.0.0-beta.0",
     "file-loader": "^1.1.11",
     "html-webpack-plugin": "^3.0.6",
     "postcss-cssnext": "^3.1.0",

yarn.lock

@@ -2791,14 +2791,14 @@ extglob@^2.0.4:
     snapdragon "^0.8.1"
     to-regex "^3.0.1"
 
-extract-text-webpack-plugin@^3.0.2:
-  version "3.0.2"
-  resolved "https://registry.yarnpkg.com/extract-text-webpack-plugin/-/extract-text-webpack-plugin-3.0.2.tgz#5f043eaa02f9750a9258b78c0a6e0dc1408fb2f7"
+extract-text-webpack-plugin@^4.0.0-beta.0:
+  version "4.0.0-beta.0"
+  resolved "https://registry.yarnpkg.com/extract-text-webpack-plugin/-/extract-text-webpack-plugin-4.0.0-beta.0.tgz#f7361d7ff430b42961f8d1321ba8c1757b5d4c42"
   dependencies:
     async "^2.4.1"
     loader-utils "^1.1.0"
-    schema-utils "^0.3.0"
-    webpack-sources "^1.0.1"
+    schema-utils "^0.4.5"
+    webpack-sources "^1.1.0"
 
 extract-zip@^1.0.3:
   version "1.6.6"
@@ -6570,12 +6570,6 @@ sax@~1.2.1:
   version "1.2.4"
   resolved "https://registry.yarnpkg.com/sax/-/sax-1.2.4.tgz#2816234e2378bddc4e5354fab5caa895df7100d9"
 
-schema-utils@^0.3.0:
-  version "0.3.0"
-  resolved "https://registry.yarnpkg.com/schema-utils/-/schema-utils-0.3.0.tgz#f5877222ce3e931edae039f17eb3716e7137f8cf"
-  dependencies:
-    ajv "^5.0.0"
-
 schema-utils@^0.4.0, schema-utils@^0.4.3:
   version "0.4.3"
   resolved "https://registry.yarnpkg.com/schema-utils/-/schema-utils-0.4.3.tgz#e2a594d3395834d5e15da22b48be13517859458e"