Update messenger-backend submodule.

CHANGELOG.md

@@ -1,6 +1,6 @@
 # Delta Chat Changelog
 
-## v0.18.1
+## v0.18.2
 2018-06-23
 
 * Fix initial configure process to hang at 95% under some circumstances

MessengerProj/build.gradle

@@ -124,7 +124,7 @@ android {
         targetSdkVersion 25  // 25: Nougat. CAVE: Do NOT target "Andoid O" without checking the background tasks carefully, see https://developer.android.com/preview/behavior-changes.html#back-all . As long as we target "Nougat", everything works as expected even for "Andoid O" or later
                              // in general, we should not change the target without reason; eg. after the switch to Nougat, the camera stops working (see https://inthecheesefactory.com/blog/how-to-share-access-to-file-with-fileprovider-on-android-nougat/en )
 
-        versionName "0.18.1" // do NOT forget to increase defaultConfig.versionCode!
-        versionCode 533
+        versionName "0.18.2" // do NOT forget to increase defaultConfig.versionCode!
+        versionCode 534
     }
 }