diff --git a/.travis.yml b/.travis.yml
index 30e9cccc30..70ebfbb908 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,9 +16,16 @@ language: python
 
 matrix:
   include:
-#    - dist: xenial  # Ubuntu 16.04
-#      python: 3.5
-#      env: TOXENV=py35
+    - dist: xenial  # Ubuntu 16.04
+      python: 3.6
+      env:
+        - TOXENV=py36
+        - MIN_REQUIREMENTS=1
+    - dist: xenial  # Ubuntu 16.04
+      python: 3.7
+      env:
+        - TOXENV=py37
+        - MIN_REQUIREMENTS=1
     - dist: bionic  # Ubuntu 18.04
       python: 3.6
       env: TOXENV=py36
@@ -51,6 +58,15 @@ install:
   - pip install future  # needed for `builtins`
   - sudo pip install tox
 
+before_script:
+  # rewrite all minimal requirements as strict
+  - if [[ "${MIN_REQUIREMENTS}" == "1" ]]; then
+      python -c "req = open('requirements.txt').read().replace('>', '=') ; open('requirements-ci.txt', 'w').write(req)" ;
+    else
+      cp requirements.txt requirements-ci.txt ;
+    fi
+  - pip install -r requirements-ci.txt -U
+
 script:
   # integration
   - tox --sitepackages
diff --git a/requirements.txt b/requirements.txt
index 48475c67ca..53f623e764 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,8 +1,8 @@
-scikit-learn==0.20.2
-tqdm==4.35.0
-numpy==1.16.4
+scikit-learn>=0.20.2
+tqdm>=4.35.0
+numpy>=1.16.4
 torch>=1.1
 torchvision>=0.3.0
-pandas>=0.20.3
+pandas>=0.24  # lower version do not support py3.7
 test-tube>=0.6.9
-# future>=0.17.1  # required for buildins in setup.py
+# future>=0.17.1  # required for buildins in setup.py
\ No newline at end of file
diff --git a/setup.cfg b/setup.cfg
index 40283b196d..366b2355e7 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -52,7 +52,7 @@ omit =
 [flake8]
 # TODO: this should be 88 or 100 according PEP8
 max-line-length = 120
-exclude = .tox,*.egg,build,temp,examples/*
+exclude = .tox,*.egg,build,temp
 select = E,W,F
 doctests = True
 verbose = 2
@@ -60,6 +60,7 @@ verbose = 2
 format = pylint
 ignore = E731,W504,F401,F841
 
+# setup.cfg or tox.ini
 [check-manifest]
 ignore =
     .travis.yml
diff --git a/tox.ini b/tox.ini
index 1db46c9b03..6f4550f532 100644
--- a/tox.ini
+++ b/tox.ini
@@ -31,11 +31,11 @@ basepython =
     py37: python3.7
     py38: python3.8
 deps =
-    -r requirements.txt
+    -r requirements-ci.txt
     -r ./tests/requirements.txt
 commands =
     pip list
-    check-manifest
+    check-manifest --ignore requirements-ci.txt
     python setup.py check --metadata --strict
     coverage run --source pytorch_lightning -m py.test pytorch_lightning tests pl_examples -v --doctest-modules
     flake8 .