dev-python/os-ken: fix dir to remove

Closes: https://bugs.gentoo.org/835877
Signed-off-by: Alessandro Barbieri <lssndrbarbieri@gmail.com>

dev-python/os-ken/os-ken-2.3.1.ebuild

@@ -48,6 +48,6 @@ BDEPEND="
 distutils_enable_tests nose
 
 src_prepare() {
-	rm -r os-ken/os-ken/tests/integrated || die
+	rm -r "${S}/os_ken/tests/integrated" || die
 	default
 }