tests: Trim .nim files trailing whitespace

via OSX: find . -name '*.nim' -exec sed -i '' -E 's/[[:space:]]+$//' {} +

tests/generics/tgenericrefs.nim

@@ -1,4 +1,4 @@
-type 
+type
   PA[T] = ref TA[T]
   TA[T] = object
     field: T
@@ -20,18 +20,18 @@ foo 23
 
 when false:
   # Compiles unless you use var a: PA[string]
-  type 
+  type
     PA = ref TA
     TA[T] = object
 
 
   # Cannot instantiate:
-  type 
+  type
     TA[T] = object
       a: PA[T]
     PA[T] = ref TA[T]
 
-  type 
+  type
     PA[T] = ref TA[T]
     TA[T] = object