build: fix system tests, move to Kokoro (#372)

diff --git a/scripts/travis.sh b/scripts/travis.sh
index 28bf5fa..2c34091 100755
--- a/scripts/travis.sh
+++ b/scripts/travis.sh
@@ -37,6 +37,6 @@
     fi
 fi
 
-# Run tox.
-echo "Running tox..."
-tox
+# Run nox.
+echo "Running nox..."
+nox
\ No newline at end of file