Error message for unknown `for` modifier includes `%q`

[osteele]

To reproduce:

template, err := ParseString("{% for item in array invalid %}{% endfor%}")
fmt.Println(err)

Expected: ""invalid" is an unknown modifier in for tag ("{% for item in array invalid %}" - line 1)"
Actual: "%q is an inknown modifier in for taginvalid (\"{% for item in array invalid %}\" - line 1)"

[C-Howard]

This issue was fixed by d1b2aa8.