Update git submodules

* Update org.eclipse.mylyn from branch 'master'
  to 6a4938659321a9d31cc30b6eba55119eacbc4a91
  - 548295: update org.eclipse.mylyn versions to 3.26
    
    Change-Id: I07fded3c9ae094858b1339899a0dfe049ec3fd95
    Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=548295 (+1 squashed commit)
    Signed-off-by: Colin Ritchie <colin.ritchie@tasktop.com>
    
diff --git a/org.eclipse.mylyn b/org.eclipse.mylyn
index c8ab476..6a49386 160000
--- a/org.eclipse.mylyn
+++ b/org.eclipse.mylyn
@@ -1 +1 @@
-Subproject commit c8ab476078da41cd2a758bb421f0b9c08bbfe821
+Subproject commit 6a4938659321a9d31cc30b6eba55119eacbc4a91