returned to 3.6 because semaphore doesn't yet support 3.7

tox.ini

@@ -2,12 +2,12 @@
 envlist =
     black
     py27
-    py37
+    py36
     doctest
     py27-regression
-    py37-regression
+    py36-regression
     py27-fuzz
-    py37-fuzz
+    py36-fuzz
     pylint
     pydocstyle
     flake8
@@ -33,7 +33,7 @@ deps =
 commands = nosetests []
 
 [testenv:doctest]
-basepython = python3.7
+basepython = python3.6
 setenv =
     NOSE_WITH_COVERAGE=0
     NOSE_WITH_DOCTEST=1
@@ -53,7 +53,7 @@ commands = nosetests {toxinidir}/tests/regression --processes=-1 \
 deps = {[testenv:regression]deps}
 commands = {[testenv:regression]commands}
 
-[testenv:py37-regression]
+[testenv:py36-regression]
 deps = {[testenv:regression]deps}
 commands = {[testenv:regression]commands}
 
@@ -66,32 +66,32 @@ commands = nosetests {toxinidir}/tests/fuzz --processes=-1 \
 deps = {[testenv:fuzz]deps}
 commands = {[testenv:fuzz]commands}
 
-[testenv:py37-fuzz]
+[testenv:py36-fuzz]
 deps = {[testenv:fuzz]deps}
 commands = {[testenv:fuzz]commands}
 
 
 [testenv:pylint]
-basepython = python3.7
+basepython = python3.6
 skip_install = true
 deps = pylint
 commands = {toxinidir}/helpers/call_and_write_log.py \
                "pylint --rcfile=setup.cfg abydos" 0
 
 [testenv:pydocstyle]
-basepython = python3.7
+basepython = python3.6
 skip_install = true
 deps = pydocstyle
 commands = {toxinidir}/helpers/call_and_write_log.py "pydocstyle --count ." 0
 
 [testenv:pycodestyle]
-basepython = python3.7
+basepython = python3.6
 skip_install = true
 deps = pycodestyle
 commands = {toxinidir}/helpers/call_and_write_log.py "pycodestyle ." 0
 
 [testenv:flake8]
-basepython = python3.7
+basepython = python3.6
 skip_install = true
 deps =
     flake8
@@ -122,14 +122,14 @@ commands = {toxinidir}/helpers/call_and_write_log.py \
                "flake8 {toxinidir} --htmldir={toxinidir}/flake8" 0
 
 [testenv:doc8]
-basepython = python3.7
+basepython = python3.6
 skip_install = true
 deps = doc8
 commands = {toxinidir}/helpers/call_and_write_log.py "doc8 {toxinidir}" 0
 
 [testenv:docs]
 changedir = docs
-basepython = python3.7
+basepython = python3.6
 whitelist_externals=make
 deps =
     sphinx
@@ -147,20 +147,20 @@ commands =
     sphinx-build -j 8 -b coverage -d {envtmpdir}/doctrees . _build/coverage
 
 [testenv:badges]
-basepython = python3.7
+basepython = python3.6
 skip_install = true
 commands = python {toxinidir}/badge_update.py
 
 [testenv:black]
 changedir = {toxinidir}
-basepython = python3.7
+basepython = python3.6
 skip_install = true
 deps = black
 commands = black .
 
 [testenv:dist]
 changedir = {toxinidir}
-basepython = python3.7
+basepython = python3.6
 skip_install = true
 commands =
     python setup.py sdist