tools/run_dev.sh: Allow specifying BAZEL

On my system, I installed bazelisk as suggested by the developer
guide.  Allow users to export BAZEL=... to specify which bazel command
they want to use to build.

Change-Id: I15c5a575e757a8f99104aa01a75c28b8c448de15

tools/run_dev.sh

diff --git a/tools/run_dev.sh b/tools/run_dev.sh
index 1f4ed5e..b045164 100755
--- a/tools/run_dev.sh
+++ b/tools/run_dev.sh
@@ -35,7 +35,7 @@
 
 (
   cd "$ROOT"
-  bazel build java/com/google/gitiles/dev
+  "${BAZEL:-bazel}" build java/com/google/gitiles/dev
 )
 
 set -x