Try adding the plugin dependency inside the plugin itself.
- <plugin>
<groupId>org.liquibase</groupId>
<artifactId>liquibase-maven-plugin</artifactId>
<version>3.3.2</version>
<configuration>
<propertyFile>src/main/resources/liquibase/liquibase.properties</propertyFile>
</configuration>
<executions>
<execution>
<phase>process-resources</phase>
<goals>
<goal>update</goal>
</goals>
</execution>
</executions>
<dependencies>
<dependency>
<groupId>com.github.adangel.liquibase.ext</groupId>
<artifactId>liquibase-percona</artifactId>
<version>1.1.0</version>
</dependency>
</dependencies>
</plugin>