fix lint error: fmt.Sprintf() on string

Fixes the following golanci-lint error:
```
printf: non-constant format string in call to fmt.Sprintf
```

Since `c.cf.TCPDomain` is a string, we can just return it without the
`fmt.Sprintf()` wrapper.

cfWorkflow/cfWorkflow.go

@@ -59,7 +59,7 @@ func (c *cfWorkflow) AppUrl() string {
 }
 
 func (c *cfWorkflow) TCPDomain() string {
-	return fmt.Sprintf(c.cf.TCPDomain)
+	return c.cf.TCPDomain
 }
 
 func (c *cfWorkflow) TCPPort() int {