build: bump prop-types from 15.6.0 to 15.6.1

Bumps [prop-types](https://github.com/facebook/prop-types) from 15.6.0 to 15.6.1.
- [Changelog](https://github.com/facebook/prop-types/blob/master/CHANGELOG.md)
- [Commits](https://github.com/facebook/prop-types/commits/v15.6.1)

package.json

@@ -44,7 +44,7 @@
     "postcss-loader": "^2.1.3",
     "postcss-smart-import": "^0.7.5",
     "precss": "^3.1.1",
-    "prop-types": "^15.5.10",
+    "prop-types": "^15.6.1",
     "rails-erb-loader": "^5.4.1",
     "raven-js": "3.24.0",
     "rc-progress": "2.2.5",

yarn.lock

@@ -5724,9 +5724,9 @@ promise@^7.1.1:
   dependencies:
     asap "~2.0.3"
 
-prop-types@^15.5.10, prop-types@^15.5.4, prop-types@^15.5.8, prop-types@^15.6.0:
-  version "15.6.0"
-  resolved "https://registry.yarnpkg.com/prop-types/-/prop-types-15.6.0.tgz#ceaf083022fc46b4a35f69e13ef75aed0d639856"
+prop-types@^15.5.10, prop-types@^15.5.4, prop-types@^15.5.8, prop-types@^15.6.0, prop-types@^15.6.1:
+  version "15.6.1"
+  resolved "https://registry.yarnpkg.com/prop-types/-/prop-types-15.6.1.tgz#36644453564255ddda391191fb3a125cbdf654ca"
   dependencies:
     fbjs "^0.8.16"
     loose-envify "^1.3.1"