Update mysql to b4242ba (latest). (#4552)

The most recent tagged release of mysql is v1.4.1, from a year ago. It
also happens to pull in an unwanted dependency (appengine) that the
latest commit does not.

Tests pass:

$ go test -count=1 github.com/go-sql-driver/mysql
ok github.com/go-sql-driver/mysql 0.068s

Fixes #4530

go.mod

@@ -9,7 +9,7 @@ require (
 	github.com/cloudflare/cfssl v1.4.0
 	github.com/eggsampler/acme/v2 v2.0.1
 	github.com/go-gorp/gorp v2.0.0+incompatible // indirect
-	github.com/go-sql-driver/mysql v1.3.1-0.20170715192408-3955978caca4
+	github.com/go-sql-driver/mysql v1.4.1-0.20191114115753-b4242bab7dc5
 	github.com/golang/mock v1.2.0
 	github.com/golang/protobuf v1.3.1
 	github.com/golang/snappy v0.0.0-20170215233205-553a64147049 // indirect

go.sum

@@ -48,6 +48,8 @@ github.com/go-sql-driver/mysql v1.3.0 h1:pgwjLi/dvffoP9aabwkT3AKpXQM93QARkjFhDDq
 github.com/go-sql-driver/mysql v1.3.0/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG5ZlKdlhCg5w=
 github.com/go-sql-driver/mysql v1.3.1-0.20170715192408-3955978caca4 h1:VR5tBQt9N1t7k1gLi3zDPVMJ7dNwrHewr8cH+r3hRCo=
 github.com/go-sql-driver/mysql v1.3.1-0.20170715192408-3955978caca4/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG5ZlKdlhCg5w=
+github.com/go-sql-driver/mysql v1.4.1-0.20191114115753-b4242bab7dc5 h1:TPdJVmaDpKVlxYKc2CTaU6iY51jeQqbRooWdI1ATYG4=
+github.com/go-sql-driver/mysql v1.4.1-0.20191114115753-b4242bab7dc5/go.mod h1:XIaZU7xtUgusUqDPXOOPcmC5Dyyw3F1pbh54fHzaehk=
 github.com/gogo/googleapis v1.1.0/go.mod h1:gf4bu3Q80BeJ6H1S1vYPm8/ELATdvryBaNFGgqEef3s=
 github.com/gogo/protobuf v1.2.0/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=