Explicitly use project.version

This addresses a Maven warning: The expression ${version} is
deprecated. Please use ${project.version} instead.

pom.xml

@@ -315,7 +315,7 @@
         <artifactId>really-executable-jar-maven-plugin</artifactId>
         <version>2.1.1</version>
         <configuration>
-          <inputFile>target/s3proxy-${version}-jar-with-dependencies.jar</inputFile>
+          <inputFile>target/s3proxy-${project.version}-jar-with-dependencies.jar</inputFile>
           <programFile>s3proxy</programFile>
         </configuration>
         <executions>