[build] upgrade vue-loader@15 (#937)

package.json

@@ -82,7 +82,7 @@
     "gh-pages": "^1.0.0",
     "html-webpack-plugin": "3.2.0",
     "husky": "^0.14.3",
-    "isparta-loader": "^2.0.0",
+    "istanbul-instrumenter-loader": "^3.0.1",
     "karma": "^2.0.0",
     "karma-chrome-launcher": "^2.2.0",
     "karma-coverage": "^1.1.1",
@@ -109,7 +109,7 @@
     "url-loader": "^1.0.1",
     "vant-doc": "1.0.4",
     "vue": "2.5.16",
-    "vue-loader": "^14.2.2",
+    "vue-loader": "^15.0.0",
     "vue-router": "^3.0.1",
     "vue-sfc-compiler": "^0.0.8",
     "vue-style-loader": "^4.1.0",