Properly capitalized Twitter (#4896)

README.md

@@ -10,7 +10,7 @@ The aim of this project is to provide a fast lightweight 2D library that works
 across all devices. The PixiJS renderer allows everyone to enjoy the power of
 hardware acceleration without prior knowledge of WebGL. Also, it's fast. Really fast.
 
-If you want to keep up to date with the latest PixiJS news then feel free to follow us on twitter
+If you want to keep up to date with the latest PixiJS news then feel free to follow us on Twitter
 ([@doormat23](https://twitter.com/doormat23), [@rolnaaba](https://twitter.com/rolnaaba), [@bigtimebuddy](https://twitter.com/bigtimebuddy), [@ivanpopelyshev](https://twitter.com/ivanpopelyshev))
 and we will keep you posted! You can also check back on [our site](http://www.pixijs.com)
 as any breakthroughs will be posted up there too!