Fixed error reporting showing 'file is not defined'

[adriantoine]

Hi!

The file variable should be set outside of the try statement because it is used in the catch error reporting. So when there's an error parsing a file I will only get:

ERROR in ./~/react-styleguidist/loaders/props.loader.js!./src/components/modal/prompt/Prompt.js
Module build failed: ReferenceError: file is not defined
    at Object.module.exports (/Users/adrien/Projects/dev-setup/tray/src/github.com/trayio/react-ui/node_modules/react-styleguidist/loaders/props.loader.js:41:66)
 @ ./~/react-styleguidist/loaders/styleguide.loader.js! 4:19905-20030
 @ ./~/react-styleguidist/src/index.js
 @ multi main

and after this fix I get the right error message:

Error when parsing src/components/modal/prompt/Prompt.js
Error: No suitable component definition found.

[sapegin]

Thanks!