tests: Trim .nim files trailing whitespace

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

tests/assert/tuserassert.nim

@@ -2,12 +2,12 @@ discard """
   output: "x == 45ugh"
 """
 
-template myAssert(cond: expr) = 
+template myAssert(cond: expr) =
   when 3 <= 3:
     let c = cond.astToStr
     if not cond:
       echo c, "ugh"
-  
+
 var x = 454
 myAssert(x == 45)