chore(deps): update dependency mongo to v2.21.2

Author: renovate[bot]

Gemfile.lock

@@ -9,7 +9,7 @@ GEM
   specs:
     base64 (0.2.0)
     bigdecimal (3.1.8)
-    bson (5.0.1)
+    bson (5.0.2)
     bson_ext (1.5.1)
     coderay (1.1.3)
     diff-lcs (1.5.1)
@@ -39,7 +39,8 @@ GEM
     logger (1.6.1)
     lumberjack (1.2.10)
     method_source (1.1.0)
-    mongo (2.21.0)
+    mongo (2.21.2)
+      base64
       bson (>= 4.14.1, < 6.0.0)
     mustermann (3.0.3)
       ruby2_keywords (~> 0.0.1)