tests: Trim .nim files trailing whitespace

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

tests/closure/uclosures.nim

@@ -2,7 +2,7 @@ import unittest
 
 test "loop variables are captured by copy":
   var funcs: seq[proc (): int {.closure.}] = @[]
-  
+
   for i in 0..10:
     let ii = i
     funcs.add do -> int: return ii * ii