Make tycho-versions-plugin's version explicit

Because:
 - I just faced issues while changing project's version due to Maven using the tycho-versions-plugin 1.3.0

Author: echebbi

pom.xml

@@ -64,6 +64,11 @@
 				<version>${tycho-version}</version>
 				<extensions>true</extensions>
 			</plugin>
+			<plugin>
+				<groupId>org.eclipse.tycho</groupId>
+				<artifactId>tycho-versions-plugin</artifactId>
+				<version>${tycho-version}</version>
+			</plugin>
 			<plugin>
 				<!-- Activate Pitclipse's target platform -->
 				<groupId>org.eclipse.tycho</groupId>