Upgrade to really-executable-jars-maven-plugin 1.4.0

Release notes:

https://github.com/brianm/really-executable-jars-maven-plugin/releases/tag/really-executable-jar-maven-plugin-1.4.0

pom.xml

@@ -204,7 +204,7 @@
       <plugin>
         <groupId>org.skife.maven</groupId>
         <artifactId>really-executable-jar-maven-plugin</artifactId>
-        <version>1.3.0</version>
+        <version>1.4.0</version>
         <configuration>
           <programFile>s3proxy</programFile>
         </configuration>