patch 8.1.1876: proto file missing from distribution

Problem:    proto file missing from distribution
Solution:   Add the file.
diff --git a/src/version.c b/src/version.c
index 2c02209..ed8cc6b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1876,
+/**/
     1875,
 /**/
     1874,