Update rust.vim

Column limit 78 -> 100.

Author: luqmana

src/etc/vim/after/ftplugin/rust.vim

@@ -1,5 +1,5 @@
-"Highlight the 78th text column
+"Highlight the 100th text column
 "Feature became available in v7.3
 if version >= 703
-    set colorcolumn=78
+    set colorcolumn=100
 endif