manifest: add omni external/aac

Change-Id: Id8e887ab64367ea2cc61b494ac5a887df9bb008f
diff --git a/omni-aosp.xml b/omni-aosp.xml
index 68d20ca..6d4f117 100644
--- a/omni-aosp.xml
+++ b/omni-aosp.xml
@@ -26,6 +26,7 @@
 
   <project path="development" name="android_development" remote="omnirom" revision="android-8.1" groups="pdk-cw-fs,pdk-fs" />
 
+  <project path="external/aac" name="android_external_aac" remote="omnirom" revision="android-8.1" />
   <project path="external/e2fsprogs" name="android_external_e2fsprogs" remote="omnirom" revision="android-8.1" />
   <project path="external/mksh" name="android_external_mksh" remote="omnirom" revision="android-8.1" />
   <project path="external/tinycompress" name="android_external_tinycompress" remote="omnirom" revision="android-8.1" />