CI: Require pip < 19.1 for Python 2.7 and 3.4

diff --git a/.travis.yml b/.travis.yml
index 88e2328ba678b28cecdee7b5f906046cf9cb1c91..68a8bace73e7e1e9c45be66f6f62028463e42a03 100644 (file)
--- a/.travis.yml
+++ b/.travis.yml
@@ -33,7 +33,7 @@ matrix:
     env: TOXENV=pypy
 
 install:
-  - travis_retry pip install --upgrade pip setuptools tox ppu
+  - travis_retry pip install --upgrade "pip < 19.1" setuptools tox ppu
 
 script:
   - tox