qjson: Handle "\f"

It's valid JSON and should be handled.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/json-parser.c b/json-parser.c
index b55d763..83212bc 100644
--- a/json-parser.c
+++ b/json-parser.c
@@ -206,6 +206,10 @@
                 qstring_append(str, "\b");
                 ptr++;
                 break;
+            case 'f':
+                qstring_append(str, "\f");
+                ptr++;
+                break;
             case 'n':
                 qstring_append(str, "\n");
                 ptr++;