Update Crashlytics to 2.6.7.

app/build.gradle

@@ -145,7 +145,7 @@ release {
 
 dependencies {
     compile files('libs/slf4j-api-1.7.2.jar')
-    compile('com.crashlytics.sdk.android:crashlytics:2.6.6@aar') {
+    compile('com.crashlytics.sdk.android:crashlytics:2.6.7@aar') {
         transitive = true;
     }
     compile('com.mikepenz:materialdrawer:5.2.9@aar') {