patch 8.0.1435: memory leak in test_arabic

Problem:    Memory leak in test_arabic.
Solution:   Free the from and to parts. (Christian Brabandt, closes #2569)
diff --git a/src/proto/digraph.pro b/src/proto/digraph.pro
index a8d2ae9..3cb7dce 100644
--- a/src/proto/digraph.pro
+++ b/src/proto/digraph.pro
@@ -6,4 +6,5 @@
 void listdigraphs(void);
 char_u *keymap_init(void);
 void ex_loadkeymap(exarg_T *eap);
+void keymap_clear(garray_T *kmap);
 /* vim: set ft=c : */