remove python versions under 3.5(included 3.5)

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index e51b4ac..e190c55 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,5 @@
 language: python

 python:

-- '3.4'

-- '3.5'

 - '3.6'

 - '3.7'

 - '3.8'