[fix] fix type error.

argotk.hs

@@ -43,9 +43,10 @@ runApp sa app = runSimpleStack $ sa {app = app}
 
 runHelloWorld :: StackArgs -> IO ()
 runHelloWorld a@StackArgs{..} = do
-  let passStr = "HelloWorldFromApp"
-  runSimpleStack $ a {app = format ("echo "%s) passStr}
-  readTextFile cmd_err >>= \x -> case match (has passStr) x of
+  let passText = "HelloWorldFromApp"
+  let passPattern = text passText
+  runSimpleStack $ a {app = format ("echo "%s) passText}
+  readTextFile cmd_err >>= \x -> case match (has passPattern) x of
     [] -> die ("Hello world app failed to run.")
     _  -> sh $ printInfo "The hello world app executed properly in a \
                          \container and its message was received by `cmd`.\n"