Run tests for python 3.7 without extra dependencies

.travis.yml

@@ -31,7 +31,7 @@ matrix:
     - python: 3.7
       dist: xenial
       sudo: true
-      env: TOXENV=py37
+      env: TOXENV=py37-nodeps
 
 addons:
     apt:

tox.ini

@@ -6,7 +6,7 @@
 ; https://github.com/Microsoft/LightGBM/tree/master/python-package#lightgbm-python-package.
 
 [tox]
-envlist = py27,py34,py35,py35-nodeps,mypy,py35-extra,py27-extra,py36,py36-extra,py36-legacy,py37
+envlist = py27,py34,py35,py35-nodeps,mypy,py35-extra,py27-extra,py36,py36-extra,py36-legacy,py37-nodeps
 
 [base]
 deps=
@@ -94,3 +94,13 @@ deps=
 changedir=docs/source
 commands=
     sphinx-build -W -b html . {envtmpdir}/html
+
+
+[testenv:py37-nodeps]
+deps=
+    {[base]deps}
+
+commands=
+    ; without lightning as it is optional
+    pip install -e .
+    bash _ci/runtests_nodeps.sh {posargs: eli5 tests}