Add ":" alongside "true" for SC2015

Author: koalaman

src/ShellCheck/Analytics.hs

@@ -890,7 +890,7 @@ checkShorthandIf params x@(T_OrIf _ (T_AndIf id _ b) (T_Pipeline _ _ t))
   where
     isOk [t] = isAssignment t || fromMaybe False (do
         name <- getCommandBasename t
-        return $ name `elem` ["echo", "exit", "return", "printf", "true"])
+        return $ name `elem` ["echo", "exit", "return", "printf", "true", ":"])
     isOk _ = False
     inCondition = isCondition $ getPath (parentMap params) x
 checkShorthandIf _ _ = return ()