Travis: run selftest on Windows

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/.travis.yml b/.travis.yml
index eb01a44..ed2910a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -70,6 +70,7 @@
       os: windows
       script:
         - scripts/windows_msbuild.bat v141 # Visual Studio 2017
+        - visualc/VS2013/x64/Release/selftest.exe
 
 after_failure:
 - tests/scripts/travis-log-failure.sh