Merge pull request #663 from mybatis/renovate/com.alibaba-druid-1.x

Update dependency com.alibaba:druid to v1.2.21

Author: hazendaz

pom.xml

@@ -165,7 +165,7 @@
     <dependency>
       <groupId>com.alibaba</groupId>
       <artifactId>druid</artifactId>
-      <version>1.2.20</version>
+      <version>1.2.21</version>
       <optional>true</optional>
       <exclusions>
         <exclusion>