Update appengine build to use JDK 1.7

Change-Id: I27191377afac5a2d01db9092934e2c4b25e639ce

appinventor/appengine/build.xml

@@ -4,7 +4,7 @@
      Copyright 2011-2012 Google Inc.  All Rights Reserved.
      Author: kerr@google.com (Debby Wallach)
      Author: lizlooney@google.com (Liz Looney)
-     Copyright © 2012-2016 Massachusetts Institute of Technology. All Rights Reserved.
+     Copyright © 2012-2017 Massachusetts Institute of Technology. All Rights Reserved.
      Author: jis@mit.edu (Jeffrey I. Schiller)
      Author: hal@mit.edu (Hal Abelson)
      Author: ram8647@gmail.com (Ralph Morelli)
@@ -198,7 +198,8 @@
     <copy todir="${AiServerLib-class.dir}/${appinventor.pkg}/server">
       <fileset dir="src/${appinventor.pkg}/server/" includes="*.properties" />
     </copy>
-    <ai.javac destdir="${AiServerLib-class.dir}" >
+    <ai.javac destdir="${AiServerLib-class.dir}"
+              source="1.7" target="1.7">
       <include name="${appinventor.pkg}/server/**/*.java" />
       <classpath>
         <!-- jars that we put in <build>/war/WEB-INF/lib -->
@@ -319,7 +320,8 @@
     <property name="AiSharedLib-class.dir" location="${class.dir}/AiSharedLib" />
     <mkdir dir="${AiSharedLib-class.dir}" />
 
-    <ai.javac destdir="${AiSharedLib-class.dir}" >
+    <ai.javac destdir="${AiSharedLib-class.dir}"
+              source="1.7" target="1.7">
       <include name="${appinventor.pkg}/shared/**/*.java" />
       <classpath>
         <!-- jars that we put in <build>/war/WEB-INF/lib -->
@@ -372,7 +374,8 @@
     <property name="AiRebindLib-class.dir" location="${class.dir}/AiRebindLib" />
     <mkdir dir="${AiRebindLib-class.dir}" />
 
-    <ai.javac destdir="${AiRebindLib-class.dir}" >
+    <ai.javac destdir="${AiRebindLib-class.dir}"
+              source="1.7" target="1.7">
       <include name="${appinventor.pkg}/rebind/**/*.java" />
       <classpath>
         <!-- gwt libs -->
@@ -400,7 +403,7 @@
     <ai.javac encoding="utf-8"
               destdir="${build.war.dir}/WEB-INF/classes"
               srcdir="${src.dir};${build.dir}/components/ComponentTranslation/src"
-              source="1.5" target="1.5" nowarn="true"
+              source="1.7" target="1.7" nowarn="true"
               debug="true" debuglevel="lines,vars,source">
       <include name="${appinventor.pkg}/client/**/*.java" />
       <include name="${appinventor.pkg}/shared/**/*.java" />