Fix parent version in some POMs

Use the correct snapshot version of the parent.

compatibility-server-gae/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>com.vaadin</groupId>
         <artifactId>vaadin-root</artifactId>
-        <version>8.0-SNAPSHOT</version>
+        <version>8.1-SNAPSHOT</version>
     </parent>
     <artifactId>vaadin-compatibility-server-gae</artifactId>
     <name>vaadin-compatibility-server-gae</name>

liferay-integration/pom.xml

@@ -9,7 +9,7 @@
     <parent>
         <groupId>com.vaadin</groupId>
         <artifactId>vaadin-root</artifactId>
-        <version>8.0-SNAPSHOT</version>
+        <version>8.1-SNAPSHOT</version>
     </parent>
 
     <properties>

osgi-integration/pom.xml

@@ -9,7 +9,7 @@
     <parent>
         <groupId>com.vaadin</groupId>
         <artifactId>vaadin-root</artifactId>
-        <version>8.0-SNAPSHOT</version>
+        <version>8.1-SNAPSHOT</version>
     </parent>
 
     <properties>