Add 17.4 support

Erlang 17.4 added a new driver entry, `emergency_close`. This
patch tests for it by driver versions and adds an initializer if
necessary. This patch also adds new Erlang versions to the Travis CI config
to test the new driver field.

.travis.yml

@@ -1,6 +1,8 @@
 language: erlang
 script: "make test"
 otp_release:
+  - 18.0
+  - 17.4
   - 17.3
   - R16B03-1
   - R15B03

c_src/sqlite3_drv.c

@@ -209,7 +209,13 @@ static ErlDrvEntry sqlite3_driver_entry = {
   ERL_DRV_FLAG_USE_PORT_LOCKING, /* ERL_DRV_FLAGs */
   NULL /* handle2 */,
   NULL /* process_exit */,
+  #if ERL_DRV_EXTENDED_MAJOR_VERSION > 3 || \
+  (ERL_DRV_EXTENDED_MAJOR_VERSION == 3 && ERL_DRV_EXTENDED_MINOR_VERSION >= 2)
+  NULL /* stop_select */,
+  NULL /* emergency_close */
+  #else
   NULL /* stop_select */
+  #endif
 };
 
 DRIVER_INIT(sqlite3_driver) {