Fix Travis CI issues

- use pip >= 19.2 (fix safety issues)
- use only 3.9-dev (3.9 is currently not available in Travis)
- run pytest from project root (coveralls.io is unable to
  access sources)

.travis.yml

@@ -5,7 +5,6 @@ python:
   - 3.6
   - 3.7
   - 3.8
-  - 3.9
   - 3.9-dev
 
 install:

tox.ini

@@ -10,27 +10,26 @@ skipsdist = True
 [testenv]
 passenv = *
 setenv =
-    PYTHONPATH=.
+    PYTHONPATH=src
 skip_install = True
 description =
     {envname}: Run unit tests for {envname}
 deps =
+    pip >= 19.2
     safety
     tox
     unittest2
     pytest
     pytest-cov
     coveralls
-changedir = src
 commands =
     safety check --full-report
-    pytest --cov=tox_lsr --cov-report=term-missing ../tests
+    pytest --cov=tox_lsr --cov-report=term-missing tests
     {env:COVERALLS_CMD:coveralls --output={envname}-coverage.txt}
 
 [linters]
 envdir = {toxworkdir}/env-{env:TRAVIS_PYTHON_VERSION:linters}
 basepython = python3.6
-changedir = {toxinidir}
 
 [testenv:black]
 envdir = {[linters]envdir}
@@ -39,7 +38,6 @@ description =
     {envname}: Run formatting checks
 deps =
     black
-changedir = {[linters]changedir}
 commands =
     black --check --diff .
 
@@ -50,7 +48,6 @@ description =
     {envname}: Run import order checks
 deps =
     isort
-changedir = {[linters]changedir}
 commands =
     isort --diff -c .
 
@@ -65,7 +62,6 @@ deps =
     tox
     unittest2
     pylint
-changedir = {[linters]changedir}
 commands =
     pylint setup.py src/tox_lsr
     pylint -d C0115,C0116,C0321,E0611,R0903,W0613 \
@@ -81,7 +77,6 @@ deps =
     flake8
     flake8-logging-format
     hacking
-changedir = {[linters]changedir}
 commands =
     flake8
 
@@ -93,7 +88,6 @@ description =
 deps =
     tox
     mypy
-changedir = {[linters]changedir}
 commands =
     mypy src/tox_lsr
 
@@ -104,7 +98,6 @@ description =
     {envname}: Run security analyzer
 deps =
     bandit
-changedir = {[linters]changedir}
 commands =
     bandit -vlir setup.py src/tox_lsr stubs tests/unit
 
@@ -115,7 +108,6 @@ description =
     {envname}: Run doc strings checks
 deps =
     pydocstyle
-changedir = {[linters]changedir}
 commands =
     pydocstyle setup.py src/tox_lsr
     pydocstyle --add-ignore=D101,D102,D103,D107 stubs tests/unit