patch 8.0.0796: no coverage on Travis with clang

Problem:    No coverage on Travis with clang.
Solution:   Use a specific coveralls version. (Ozaki Kiichi, closes #1888)
diff --git a/src/version.c b/src/version.c
index 49d553f..9ca8700 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    796,
+/**/
     795,
 /**/
     794,