Added in a .bazelversion file to work with Bazelisk

Change-Id: I420e895c31f50b3fc065c6edffbffaa5793a56f8
diff --git a/.bazelversion b/.bazelversion
new file mode 100644
index 0000000..6085e94
--- /dev/null
+++ b/.bazelversion
@@ -0,0 +1 @@
+1.2.1