versioner: improve error output slightly.

Print [introduced = 9, deprecated = 10, obsoleted = 11] instead of
[9,10,11].

Change-Id: Ifb8a66abbcec92aa13086d220af7ee6fa17b0897
diff --git a/tools/versioner/src/versioner.cpp b/tools/versioner/src/versioner.cpp
index 91482ed..fcef6b1 100644
--- a/tools/versioner/src/versioner.cpp
+++ b/tools/versioner/src/versioner.cpp
@@ -318,7 +318,7 @@
       // Make sure that availability declarations are consistent across API levels for a given arch.
       if (last_availability != current_availability) {
         error = true;
-        printf("%s: availability mismatch between %s and %s: %s before, %s after\n",
+        printf("%s: availability mismatch between %s and %s: [%s] before, [%s] after\n",
                symbol_name.c_str(), last_type.describe().c_str(), type.describe().c_str(),
                last_availability.describe().c_str(), current_availability.describe().c_str());
       }