Bug 568875 - Update JDT and Platform porting guide links for 4.18 in Welcome page

Change-Id: I2716643007bfaca8560ae31460fdd765141ead33
Signed-off-by: Kalyan Prasad Tatavarthi <kalyan_prasad@in.ibm.com>
diff --git a/org.eclipse.jdt/intro/migrateExtensionContent.xml b/org.eclipse.jdt/intro/migrateExtensionContent.xml
index 22ddf5f..9684adb 100644
--- a/org.eclipse.jdt/intro/migrateExtensionContent.xml
+++ b/org.eclipse.jdt/intro/migrateExtensionContent.xml
@@ -3,8 +3,8 @@
   <!-- Extension to the SDK Migration Page. -->
   <extensionContent id="org.eclipse.jdt" name="Java development tools" alt-style="css/migrate.properties" style="css/migrate.css" path="migrate/@">
      <group id="content-group" style-id="content-group">
-    	<link style-id="content-link" label="Java development tools" url="http://org.eclipse.ui.intro/showHelpTopic?id=/org.eclipse.jdt.doc.isv/porting/eclipse_4_17_porting_guide.html" id="java">
-      		<text>Eclipse JDT 4.17 Plug-in Migration Guide</text>
+    	<link style-id="content-link" label="Java development tools" url="http://org.eclipse.ui.intro/showHelpTopic?id=/org.eclipse.jdt.doc.isv/porting/eclipse_4_18_porting_guide.html" id="java">
+      		<text>Eclipse JDT 4.18 Plug-in Migration Guide</text>
     	</link>
      </group>
   </extensionContent>