[expo-docs] Fix mimetype image/jpg to image/jpeg
[expo-docs] Fix mimetype image/jpg to image/jpeg

Closes expo/expo-docs#148

exponentjs/exponent,exponent/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent