Only include "[a-z]*.bash" files for completion

Some people were using case-insensitive filesystems which broke when
including simply [a-z]* since it matched the uppercase files. Use this
to filter only the actual bash scripts.

Change-Id: Ibfdcf2c091a154f0485545537a044667783a19f7
diff --git a/envsetup.sh b/envsetup.sh
index e79fa28..f1e7101 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -197,7 +197,7 @@
 
     dir="sdk/bash_completion"
     if [ -d ${dir} ]; then
-        for f in ${dir}/[a-z]*; do
+        for f in ${dir}/[a-z]*.bash; do
             echo "including $f"
             . $f
         done