build(deps): upgrade webpack version to ^4.36.0

Webpack 4.36.0 is the minimum version that sass-loader 8 requires.

- 4.20.0 has been released in september 2018: https://github.com/webpack/webpack/releases/tag/v4.20.0
- 4.36.0 has been released in july 2019: https://github.com/webpack/webpack/releases/tag/v4.36.0

package.json

@@ -46,7 +46,7 @@
     "style-loader": "^1.1.3",
     "terser-webpack-plugin": "^1.1.0",
     "tmp": "^0.2.1",
-    "webpack": "^4.20.0",
+    "webpack": "^4.36.0",
     "webpack-cli": "^3.0.0",
     "webpack-dev-server": "^3.1.14",
     "webpack-manifest-plugin": "^2.0.2",

yarn.lock

@@ -8780,16 +8780,16 @@ webpack-sources@^1.1.0, webpack-sources@^1.3.0, webpack-sources@^1.4.0, webpack-
     source-list-map "^2.0.0"
     source-map "~0.6.1"
 
-webpack@^4.20.0:
-  version "4.43.0"
-  resolved "https://registry.yarnpkg.com/webpack/-/webpack-4.43.0.tgz#c48547b11d563224c561dad1172c8aa0b8a678e6"
-  integrity sha512-GW1LjnPipFW2Y78OOab8NJlCflB7EFskMih2AHdvjbpKMeDJqEgSx24cXXXiPS65+WSwVyxtDsJH6jGX2czy+g==
+webpack@^4.36.0:
+  version "4.42.1"
+  resolved "https://registry.yarnpkg.com/webpack/-/webpack-4.42.1.tgz#ae707baf091f5ca3ef9c38b884287cfe8f1983ef"
+  integrity sha512-SGfYMigqEfdGchGhFFJ9KyRpQKnipvEvjc1TwrXEPCM6H5Wywu10ka8o3KGrMzSMxMQKt8aCHUFh5DaQ9UmyRg==
   dependencies:
     "@webassemblyjs/ast" "1.9.0"
     "@webassemblyjs/helper-module-context" "1.9.0"
     "@webassemblyjs/wasm-edit" "1.9.0"
     "@webassemblyjs/wasm-parser" "1.9.0"
-    acorn "^6.4.1"
+    acorn "^6.2.1"
     ajv "^6.10.2"
     ajv-keywords "^3.4.1"
     chrome-trace-event "^1.0.2"
@@ -8806,7 +8806,7 @@ webpack@^4.20.0:
     schema-utils "^1.0.0"
     tapable "^1.1.3"
     terser-webpack-plugin "^1.4.3"
-    watchpack "^1.6.1"
+    watchpack "^1.6.0"
     webpack-sources "^1.4.1"
 
 websocket-driver@>=0.5.1: