[gardening] Use "{let,var} c: C" instead of "{let,var} c : C"

Inspired by @gribozavr:s fix in 1ad666742e

benchmark/single-source/DictTest.swift

@@ -153,7 +153,7 @@ class Box<T : Hashable where T : Equatable> : Hashable {
     value = v
   }
 
-  var hashValue : Int {
+  var hashValue: Int {
     return value.hashValue
   }
 }