Please add prop-types package into dependencies
After executing `npm install`, i built my project, and there is some errors as follow. So, maybe you should put prop-types in dependencies.
```
[0] ERROR in ./~/react-color/lib/components/block/Block.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/block
[0]  @ ./~/react-color/lib/components/block/Block.js 12:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/circle/Circle.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/circle
[0]  @ ./~/react-color/lib/components/circle/Circle.js 12:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/chrome/Chrome.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/chrome
[0]  @ ./~/react-color/lib/components/chrome/Chrome.js 12:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/github/Github.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/github
[0]  @ ./~/react-color/lib/components/github/Github.js 12:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/compact/Compact.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/compact
[0]  @ ./~/react-color/lib/components/compact/Compact.js 12:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/photoshop/Photoshop.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/photoshop
[0]  @ ./~/react-color/lib/components/photoshop/Photoshop.js 14:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/sketch/Sketch.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/sketch
[0]  @ ./~/react-color/lib/components/sketch/Sketch.js 12:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/swatches/Swatches.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/swatches
[0]  @ ./~/react-color/lib/components/swatches/Swatches.js 12:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/twitter/Twitter.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/twitter
[0]  @ ./~/react-color/lib/components/twitter/Twitter.js 12:17-38
[0] 
[0] ERROR in ./~/react-color/lib/components/sketch/SketchPresetColors.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/lib/components/sketch
[0]  @ ./~/react-color/lib/components/sketch/SketchPresetColors.js 14:17-38
[0] 
[0] ERROR in ./~/react-color/modules/react-material-design/lib/components/Raised.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/modules/react-material-design/lib/components
[0]  @ ./~/react-color/modules/react-material-design/lib/components/Raised.js 14:17-38
[0] 
[0] ERROR in ./~/react-color/modules/react-material-design/lib/components/Tab.js
[0] Module not found: Error: Cannot resolve module 'prop-types' in /src/node_modules/react-color/modules/react-material-design/lib/components
[0]  @ ./~/react-color/modules/react-material-design/lib/components/Tab.js 13:17-38
```