Rollback to rocksdb 5.15.10 (#1279)

Testing shows that the memory growth of 5.17.2 tends to exceed the
memory of a t3.large amazon instance.  Not sure if it is a misconfigured
cache, leaked native/java resource, or a deep rocksdb leak.  But rolling
back increased stability.

Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

gradle/versions.gradle

@@ -35,10 +35,10 @@ dependencyManagement {
 
     dependency 'io.pkts:pkts-core:3.0.4'
 
-    dependency "io.prometheus:simpleclient:0.6.0"
-    dependency "io.prometheus:simpleclient_common:0.6.0"
-    dependency "io.prometheus:simpleclient_hotspot:0.6.0"
-    dependency "io.prometheus:simpleclient_pushgateway:0.6.0"
+    dependency 'io.prometheus:simpleclient:0.6.0'
+    dependency 'io.prometheus:simpleclient_common:0.6.0'
+    dependency 'io.prometheus:simpleclient_hotspot:0.6.0'
+    dependency 'io.prometheus:simpleclient_pushgateway:0.6.0'
 
     dependency 'io.reactivex.rxjava2:rxjava:2.2.7'
 
@@ -73,7 +73,7 @@ dependencyManagement {
     dependency 'org.openjdk.jmh:jmh-core:1.21'
     dependency 'org.openjdk.jmh:jmh-generator-annprocess:1.21'
 
-    dependency 'org.rocksdb:rocksdbjni:5.17.2'
+    dependency 'org.rocksdb:rocksdbjni:5.15.10'
 
     dependency 'org.springframework.security:spring-security-crypto:5.1.4.RELEASE'