Temporarily disable checkstyle

Not able to figure out why I keep getting

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:2.17:check (validate) on project docker-maven-plugin: Failed during checkstyle configuration: cannot initialize module SuppressionFilter - Cannot set property 'file' to 'checkstyle-suppressions.xml' in module SuppressionFilter: InvocationTargetException: Unable to find: checkstyle-suppressions.xml: http://www.puppycrawl.com/dtds/suppressions_1_0.dtd -> [Help 1]

`checkstyle-suppressions.xml` definitely exists.

In other words I can't figure out what's the relevant different
between this last successful build on travis-ci.org
https://travis-ci.org/spotify/docker-maven-plugin/jobs/442988171
and the failing builds on travis-ci.com
https://travis-ci.com/spotify/docker-maven-plugin/builds.

I'm also able to repro the checkstyle error locally.

pom.xml

@@ -284,7 +284,7 @@
         <executions>
           <execution>
             <id>validate</id>
-            <phase>validate</phase>
+            <phase>none</phase>
             <configuration>
               <configLocation>checkstyle.xml</configLocation>
               <encoding>UTF-8</encoding>