leak canary: bump 2.9.1 (#6318)

Author: RingerJK

gradle/dependencies.gradle

@@ -46,7 +46,7 @@ ext {
       constraintLayout          : '1.1.3',
       mockito                   : '2.23.4',
       mockkVersion              : '1.12.1',
-      leakCanaryVersion         : '2.7',
+      leakCanaryVersion         : '2.9.1',
       commonsIO                 : '2.6',
       robolectric               : '4.7.3',
       mockwebserver             : '4.9.0',