Update osx documentation (3453) (#3530)

As specified here: https://github.com/apache/incubator-heron/issues/3452#issuecomment-625435818, heron now requires bazel version 3.0.0
diff --git a/website2/docs/compiling-osx.md b/website2/docs/compiling-osx.md
index 695a88a..57d88af 100644
--- a/website2/docs/compiling-osx.md
+++ b/website2/docs/compiling-osx.md
@@ -34,7 +34,7 @@
 
 ### Step 2 -- Install Bazel
 ```bash
-wget -O /tmp/bazel.sh https://github.com/bazelbuild/bazel/releases/download/0.26.0/bazel-0.26.0-installer-darwin-x86_64.sh
+wget -O /tmp/bazel.sh https://github.com/bazelbuild/bazel/releases/download/3.0.0/bazel-3.0.0-installer-darwin-x86_64.sh
 chmod +x /tmp/bazel.sh
 /tmp/bazel.sh --user
 ```