Propagate vslatestinstalled feature to libsimpleservo.

ports/libsimpleservo/api/Cargo.toml

@@ -50,6 +50,7 @@ no-wgl = ["libservo/no-wgl"]
 oculusvr = ["libservo/oculusvr"]
 profilemozjs = ["libservo/profilemozjs"]
 refcell_backtrace = ["libservo/refcell_backtrace"]
-webdriver = ["libservo/webdriver"]
 uwp = ["libservo/uwp", "webxr/openxr-api"]
+vslatestinstalled = ["libservo/vslatestinstalled"]
+webdriver = ["libservo/webdriver"]
 webgl_backtrace = ["libservo/webgl_backtrace"]

ports/libsimpleservo/capi/Cargo.toml

@@ -46,5 +46,6 @@ oculusvr = ["simpleservo/oculusvr"]
 profilemozjs = ["simpleservo/profilemozjs"]
 refcell_backtrace = ["simpleservo/refcell_backtrace"]
 uwp = ["simpleservo/uwp"]
+vslatestinstalled = ["simpleservo/vslatestinstalled"]
 webdriver = ["simpleservo/webdriver"]
 webgl_backtrace = ["simpleservo/webgl_backtrace"]