make it compile with modern Erlang (22.0)

... also do away with our local outdated copy of exprecs and use
upstream
diff --git a/rebar.config b/rebar.config
index 8e5debe..ce167ec 100644
--- a/rebar.config
+++ b/rebar.config
@@ -1,6 +1,8 @@
 {erl_opts, [debug_info]}.
 {sub_dirs, ["rel"]}. 
 {deps, [
-        {epcap, "0.7.9", {git, "https://github.com/msantos/epcap", {branch, "master"}}}
+        {pkt, ".*", {git, "https://github.com/msantos/pkt", {branch, "master"}}},
+        {epcap, "0.7.9", {git, "https://github.com/msantos/epcap", {branch, "master"}}},
+        {parse_trans, ".*", {git, "https://github.com/uwiger/parse_trans", {branch, "master"}}}
 	]}.
 {eunit_opts, [verbose, {report,{eunit_surefire,[{dir,"."}]}}]}.