bump libbson to 1.6.0-rc0

ajdavis · ajdavis · commit 1984a6e14280 · 2017-01-30T17:15:20.000-05:00
diff --git a/src/libbson b/src/libbson
@@ -1 +1 @@
-Subproject commit e83e9d833c8a8fae269404567b00561eb42404fd
+Subproject commit a893d621f1cfc3e4844ccd0589b0a0976ff1287e
