removed extra parenthesis (#90)

Author: Liable5607

src/Tutorial/Dependent.md

@@ -40,7 +40,7 @@ Before we proceed to our example, first consider how Idris recursively
 defines the natural numbers (here affixed with apostrophes to avoid introducing
 a conflict with the actual definition of `Nat`, which you can find
 [here](https://github.com/idris-lang/Idris-dev/blob/master/libs/prelude/Prelude/Nat.idr)
-for reference)):
+for reference):
 
 ```idris
 data Nat' : Type where