Fixes typo in proto_library docs
Add _'s in proto.transitivedescriptorsets
RELNOTES: none
@@ -102,7 +102,7 @@ public final class BazelProtoLibraryRule implements RuleDefinition {
<p>It only contains information about the <code>.proto</code> files directly mentioned by a
<code>proto_library</code> rule; the collection of transitive descriptor sets is available through
-the <code>proto.transitivedescriptorsets</code> Skylark provider.
+the <code>proto.transitive_descriptor_sets</code> Skylark provider.
See documentation in <code>ProtoSourcesProvider.java</code>.</p>
<!-- #END_BLAZE_RULE -->*/
