Update docs build links (#476)

Signed-off-by: Constance Caramanolis <ccaramanolis@lyft.com>

CONTRIBUTING.md

@@ -37,8 +37,8 @@ The following high level procedure is used to make Envoy changes that require AP
       ./ci/run_envoy_docker.sh './ci/do_ci.sh bazel.test'
       ./ci/run_envoy_docker.sh './ci/do_ci.sh bazel.docs'
       ```
-      *Note: New .proto files should be also included to [build.sh](https://github.com/envoyproxy/data-plane-api/blob/931aaabad939ecb1feeeaf7fbe41be15c47048d3/docs/build.sh#L28) and
-      [BUILD](https://github.com/envoyproxy/data-plane-api/blob/931aaabad939ecb1feeeaf7fbe41be15c47048d3/api/BUILD#L389) in order to get the RSTs generated.*
+      *Note: New .proto files should be also included to [build.sh](https://github.com/envoyproxy/data-plane-api/blob/4e533f22baced334c4aba68fb60c5fc439f0fe9c/docs/build.sh#L28) and
+      [BUILD](https://github.com/envoyproxy/data-plane-api/blob/master/docs/BUILD) in order to get the RSTs generated.*
 
 3. All configuration changes should have temporary associated documentation. Fields should be
    hidden from the documentation via the `[#not-implemented-hide:]` comment tag. E.g.,