update .travis.yml and run_tests.sh

- add python3.8 and pypy3 builds
- remove deprecated 'sudo: true' and 'sudo: false'
- enable builds for 'test-...' branches

scripts/run_tests.sh

@@ -1,14 +1,16 @@
 #!/bin/bash
 
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+
 TESTS_CORE=(config cookies downloader extractor oauth text util)
 TESTS_RESULTS=(results)
 
 
 # select tests
-TESTS=()
-case "${GALLERYDL_TESTS}" in
+case "${1:-${GALLERYDL_TESTS:-core}}" in
     core)    TESTS=( ${TESTS_CORE[@]}    );;
     results) TESTS=( ${TESTS_RESULTS[@]} );;
+    *)       TESTS=(                     );;
 esac
 
 
@@ -19,4 +21,4 @@ TESTS=( ${TESTS[@]/%/.py}   )
 
 # run 'nosetests' with selected tests
 # (or all tests if ${TESTS} is empty)
-nosetests --verbose -w test ${TESTS[@]}
+nosetests --verbose -w "${DIR}/../test" ${TESTS[@]}