tests: Trim .nim files trailing whitespace

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

tests/generics/tinferredgenericprocs.nim

@@ -8,7 +8,7 @@ discard """
 # https://github.com/Araq/Nim/issues/797
 proc foo[T](s:T):string = $s
 
-type IntStringProc = proc(x: int): string 
+type IntStringProc = proc(x: int): string
 
 var f1 = IntStringProc(foo)
 var f2: proc(x: int): string = foo