tests: Trim .nim files trailing whitespace

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

tests/exception/tfinally.nim

@@ -4,14 +4,14 @@ discard """
 """
 # Test return in try statement:
 
-proc main: int = 
+proc main: int =
   try:
     try:
       return 1
     finally:
       echo("came")
       return 2
-  finally: 
+  finally:
     echo("here")
     return 3