FEATURE: mini_sql upgrade

- Fixes deprecation regarding usage of BigDecimal in dev
- Handle edge case where query_hash would clear a non existent result
- Minor perf improvement to query_single

Most important thing though is that we are now on the latest gem

Gemfile.lock

@@ -205,7 +205,7 @@ GEM
       libv8 (>= 6.3)
     mini_scheduler (0.9.1)
       sidekiq
-    mini_sql (0.1.10)
+    mini_sql (0.2.1)
     mini_suffix (0.3.0)
       ffi (~> 1.9)
     minitest (5.11.3)

lib/mini_sql_multisite_connection.rb

@@ -1,4 +1,4 @@
-class MiniSqlMultisiteConnection < MiniSql::Connection
+class MiniSqlMultisiteConnection < MiniSql::Postgres::Connection
 
   class CustomBuilder < MiniSql::Builder