chore: bump ecql version to 0.7.0

PR: https://github.com/emqx/ecql/pull/13
No functional changes, just switch gen_fsm to gen_statem.

apps/emqx_bridge_cassandra/rebar.config

@@ -2,7 +2,7 @@
 
 {erl_opts, [debug_info]}.
 {deps, [
-    {ecql, {git, "https://github.com/emqx/ecql.git", {tag, "v0.6.1"}}},
+    {ecql, {git, "https://github.com/emqx/ecql.git", {tag, "v0.7.0"}}},
     {emqx_connector, {path, "../../apps/emqx_connector"}},
     {emqx_resource, {path, "../../apps/emqx_resource"}},
     {emqx_bridge, {path, "../../apps/emqx_bridge"}}