patch 8.1.1923: some source files are not in a normal encoding

Problem:    Some source files are not in a normal encoding.
Solution:   Convert hangulin.c from euc-kr to utf-8 and digraph.c from latin1
            to utf-8. (Daniel Hahler, closes #4731)
diff --git a/.travis.yml b/.travis.yml
index 085d3c5..9c184f3 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -96,7 +96,7 @@
       - do_test() { "$@"; }
 
   coverage: &coverage
-    - ~/.local/bin/coveralls -b "${SRCDIR}" -x .xs -e "${SRCDIR}"/if_perl.c -e "${SRCDIR}"/xxd -e "${SRCDIR}"/libvterm --encodings utf-8 latin-1 EUC-KR
+    - ~/.local/bin/coveralls -b "${SRCDIR}" -x .xs -e "${SRCDIR}"/if_perl.c -e "${SRCDIR}"/xxd -e "${SRCDIR}"/libvterm --encodings utf-8
     - (cd "${SRCDIR}" && bash <(curl -s https://codecov.io/bash))
 
   asan_symbolize: &asan_symbolize