Move to latest yarn (1.13)

Author: mattgodbolt

package.json

@@ -59,7 +59,7 @@
     "vis": "4.20.1",
     "winston": "^2.4.0",
     "wolfy87-eventemitter": "^5.2.3",
-    "yarn": "^1.7.0"
+    "yarn": "^1.13.0"
   },
   "devDependencies": {
     "aws-sdk-mock": "^1.7.0",

yarn.lock

@@ -6147,6 +6147,6 @@ yargs@~3.10.0:
     decamelize "^1.0.0"
     window-size "0.1.0"
 
-yarn@^1.7.0:
-  version "1.7.0"
-  resolved "https://registry.yarnpkg.com/yarn/-/yarn-1.7.0.tgz#0076b9fde6010e01950526a609bc53bc175ef925"
+yarn@^1.13.0:
+  version "1.13.0"
+  resolved "https://registry.yarnpkg.com/yarn/-/yarn-1.13.0.tgz#affa9c956739548024068532a902cf18c9cb523f"