Quote QuickJS path

We used to quote the spawnkiller path like this to handle spaces in paths:

```
 "\"" ++ filename:join(PrivDir, "couchspawnkillable") ++ "\""
```

So we stick with the same pattern here as well for QuickJS path.
diff --git a/src/couch_quickjs/src/couch_quickjs.erl b/src/couch_quickjs/src/couch_quickjs.erl
index 94307f6..8c7a225 100644
--- a/src/couch_quickjs/src/couch_quickjs.erl
+++ b/src/couch_quickjs/src/couch_quickjs.erl
@@ -26,12 +26,12 @@
 mainjs_cmd() ->
     Path = filename:join([priv_dir(), "couchjs_mainjs" ++ ext()]),
     check_path(Path),
-    apply_config(Path).
+    apply_config("\"" ++ Path ++ "\"").
 
 coffee_cmd() ->
     Path = filename:join([priv_dir(), "couchjs_coffee" ++ ext()]),
     check_path(Path),
-    apply_config(Path).
+    apply_config("\"" ++ Path ++ "\"").
 
 priv_dir() ->
     case code:priv_dir(couch_quickjs) of
diff --git a/src/couch_quickjs/test/couch_quickjs_tests.erl b/src/couch_quickjs/test/couch_quickjs_tests.erl
index c29172e..b1089e3 100644
--- a/src/couch_quickjs/test/couch_quickjs_tests.erl
+++ b/src/couch_quickjs/test/couch_quickjs_tests.erl
@@ -36,13 +36,11 @@
 
 t_get_mainjs_cmd(_) ->
     Cmd = couch_quickjs:mainjs_cmd(),
-    ?assert(filelib:is_file(Cmd)),
-    ?assertEqual("quickjs", os_cmd(Cmd ++ " -V")).
+    ?assertEqual(0, os_cmd(Cmd ++ " -V")).
 
 t_get_coffee_cmd(_) ->
     Cmd = couch_quickjs:coffee_cmd(),
-    ?assert(filelib:is_file(Cmd)),
-    ?assertEqual("quickjs", os_cmd(Cmd ++ " -V")).
+    ?assertEqual(0, os_cmd(Cmd ++ " -V")).
 
 t_can_configure_memory_limit(_) ->
     Limit = integer_to_list(4 * 1024 * 1024),
@@ -51,7 +49,7 @@
     ?assert(is_list(Cmd)),
     Expect = "-M " ++ Limit,
     ?assertEqual(Expect, string:find(Cmd, Expect)),
-    ?assertEqual("quickjs", os_cmd(Cmd ++ " -V")).
+    ?assertEqual(0, os_cmd(Cmd ++ " -V")).
 
 t_bad_memory_limit(_) ->
     Limit = integer_to_list(42),
@@ -60,9 +58,11 @@
     ?assert(is_list(Cmd)),
     ExpectCmd = "-M " ++ Limit,
     ?assertEqual(ExpectCmd, string:find(Cmd, ExpectCmd)),
-    Res = os_cmd(Cmd ++ " -V"),
-    ExpectRes = "Invalid stack size",
-    ?assertEqual(ExpectRes, string:find(Res, ExpectRes)).
+    ?assertEqual(1, os_cmd(Cmd ++ " -V")).
 
 os_cmd(Cmd) ->
-    string:trim(os:cmd(Cmd)).
+    Opts = [stream, {line, 4096}, binary, exit_status, hide],
+    Port = open_port({spawn, Cmd}, Opts),
+    receive
+        {Port, {exit_status, Status}} -> Status
+    end.