fix, minor grammar. first-class citizen (#576)

* fix, minor grammar. first-class citizen

I'd think that 'It has a [...] support.' does not sound right.
So either; 1) 'It has a first-class citizens' support', or 2) 'It has first-class citizen support' may fit better?
Option 2) technically means that first-class citizens support it. So I guess option 1) is the way to go. 
I'm not a native english speaker, so forgive me for wasting your time if I'm wrong altogether.
Cheers!

* Update typescript-support.md

Author: bambalamm

src/guide/typescript-support.md

@@ -4,7 +4,7 @@
 
 ## Official Declaration in NPM Packages
 
-A static type system can help prevent many potential runtime errors as applications grow, which is why Vue 3 is written in TypeScript. This means you don't need any additional tooling to use TypeScript with Vue - it has a first-class citizen support.
+A static type system can help prevent many potential runtime errors as applications grow, which is why Vue 3 is written in TypeScript. This means you don't need any additional tooling to use TypeScript with Vue - it has first-class citizen support.
 
 ## Recommended Configuration