doc: fix reference to buck autocomplete bash script

buck autocompletion filename[1] contains '-' instead of '_'

[1] https://github.com/facebook/buck/blob/master/scripts/buck-completion.bash

Change-Id: Ib0b7dc1359c8ab4f9a36f2f4a0ded475fc7f449d
diff --git a/Documentation/dev-buck.txt b/Documentation/dev-buck.txt
index 821868d..53f5c32 100644
--- a/Documentation/dev-buck.txt
+++ b/Documentation/dev-buck.txt
@@ -47,7 +47,7 @@
 ----
 
 To enable autocompletion of buck commands, install the autocompletion
-script from `./scripts/buck_completion.bash` in the buck project.  Refer
+script from `./scripts/buck-completion.bash` in the buck project.  Refer
 to the script's header comments for installation instructions.
 
 == Prerequisites