Merge pull request #6255 from stanley-cheung/fix-buildgen-plugin-comment

Fix buildgen plugin file comment
diff --git a/tools/buildgen/plugins/expand_version.py b/tools/buildgen/plugins/expand_version.py
index dd77f7a..c6cc562 100755
--- a/tools/buildgen/plugins/expand_version.py
+++ b/tools/buildgen/plugins/expand_version.py
@@ -27,10 +27,10 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-"""Buildgen .proto files list plugin.
+"""Buildgen package version plugin
 
 This parses the list of targets from the yaml build file, and creates
-a list called "protos" that contains all of the proto file names.
+a custom version string for each language's package.
 
 """