Keep component name after minify in build

[Sheile]

After 2.8.3, The component name will be minified by webpack in build.
Therefore, Current version of react-collapsible has following problems.

This PR will resolve it.

1. Component name in React Developer Tools is minified

Until 2.8.0, The component name is Collapsible, but current component name is s after 2.8.3.
IMO, This name may be changed unexpectedly due to changes of webpack behavior and variable name in minification.

2. Can't find component in unittest with enzyme

After 2.8.3, following test code will fail. Because component.find('Collapsible') can't find component.

expect(component.find('Collapsible').prop('open')).toBeTruthy()