Update tycho to 0.20.0, otherwise JavaSE-1.8 is not recognized as an execution environment.

fortiss-std-env/maven-build/master-pom.xml

@@ -29,7 +29,7 @@
         	<testFailureIgnore>true</testFailureIgnore>
 		    <useUIHarness>true</useUIHarness>
 		    <useUIThread>false</useUIThread>
-		    <argLine>-Xms256m -Xmx512m -XX:MaxPermSize=256M</argLine>
+		    <argLine>-Xms256m -Xmx512m</argLine>
 		    <includes>
 		       <include>**/AllTests.java</include>
 		    </includes>
@@ -59,7 +59,7 @@
     									tycho-packaging-plugin
     								</artifactId>
     								<versionRange>
-    									[0.18.0,)
+    									[0.20.0,)
     								</versionRange>
     								<goals>
     									<goal>build-qualifier</goal>
@@ -78,7 +78,7 @@
     									tycho-compiler-plugin
     								</artifactId>
     								<versionRange>
-    									[0.18.0,)
+    									[0.20.0,)
     								</versionRange>
     								<goals>
     									<goal>compile</goal>