.travis.yml: install pytest for tests, don't use explicit version

Author: twaugh

.travis.yml

@@ -5,6 +5,7 @@ before_install:
   - "sudo apt-get update -qq"
 install:
   - "sudo apt-get install -y intltool xmlto desktop-file-utils libcups2-dev"
+  - "pip install pytest"
 script: ./bootstrap && ./configure && make && make check && make distcheck
 notifications:
   email: false

Makefile.am

@@ -388,7 +388,7 @@ test-xml-validity.sh:	FORCE
 
 py.test.sh:	FORCE
 	echo "#!/bin/bash" > "$@"
-	echo "exec py.test-3.4" >> "$@"
+	echo "exec ${PYTEST-py.test}" >> "$@"
 	chmod 755 "$@"
 
 TESTS = test-xml-validity.sh py.test.sh