patch 8.0.0931: getwininfo() does not indicate a terminal window

Problem:    getwininfo() does not indicate a terminal window.
Solution:   Add "terminal" to the dictionary.

runtime/doc/eval.txt

@@ -4747,6 +4747,8 @@ getwininfo([{winid}])					*getwininfo()*
 					{only with the +quickfix feature}
 			quickfix	1 if quickfix or location list window
 					{only with the +quickfix feature}
+			terminal	1 if a terminal window
+					{only with the +terminal feature}
 			tabnr		tab page number
 			variables	a reference to the dictionary with
 					window-local variables