deb: fix fish completion install location

It looks like `completions` is owned by Fish itself. Third party
completions should go in `vendor_completions.d`.

Fixes #1485

CHANGELOG.md

@@ -39,6 +39,9 @@ Bug fixes:
   Document usage of `--type all`.
 * [BUG #1445](https://github.com/BurntSushi/ripgrep/issues/1445):
   ripgrep now respects ignore rules from .git/info/exclude in worktrees.
+* [BUG #1485](https://github.com/BurntSushi/ripgrep/issues/1485):
+  Fish shell completions from the release Debian package are now installed to
+  `/usr/share/fish/vendor_completions.d/rg.fish`.
 
 
 11.0.2 (2019-08-01)

Cargo.toml

@@ -101,7 +101,7 @@ assets = [
   ["deployment/deb/rg.1", "usr/share/man/man1/rg.1", "644"],
   # Similarly for shell completions.
   ["deployment/deb/rg.bash", "usr/share/bash-completion/completions/rg", "644"],
-  ["deployment/deb/rg.fish", "usr/share/fish/completions/rg.fish", "644"],
+  ["deployment/deb/rg.fish", "usr/share/fish/vendor_completions.d/rg.fish", "644"],
   ["deployment/deb/_rg", "usr/share/zsh/vendor-completions/", "644"],
 ]
 extended-description = """\