small efficiency improvement

Co-authored-by: zerbina <100542850+zerbina@users.noreply.github.com>

Author: saem

tools/dust/spec.nim

@@ -70,7 +70,7 @@ proc next*(remains: Remains): PNode =
 
 proc massageMessage*(s: string): string =
   result = s.splitLines()[0]
-  for c in {';', ':'}:
+  for c in [';', ':']:
     let i = find(result, c)
     if i != -1:
       result = result[0 .. i - 1]