fixed some versions in requirements_dev.txt

requirements_dev.txt

@@ -1,21 +1,21 @@
-pip==8.1.2
+pip>=9.0,<10.0
 bumpversion==0.5.3
 wheel==0.29.0
 watchdog==0.8.3
-flake8==2.6.0
+flake8>=3.4,<4.0
 tox==2.3.1
 coverage==4.1
-Sphinx==1.6
-sphinx-rtd-theme==0.2
+Sphinx>=1.6,<1.7
+sphinx-rtd-theme>=0.2,<0.3
 cryptography==1.7
 PyYAML==3.11
 
-Click>=6.0
-bokeh>=0.12
-ipython>=5.0
-ipywidgets>=5.0
-notebook>=5.0
-numpy>=1.11
-pandas>=0.19
-seaborn>=0.7
-statsmodels>=0.8
+Click>=6.0,<7.0
+bokeh>=0.12,<0.13
+ipython>=5.0,<7.0
+ipywidgets>=5.0,<7.0
+notebook>=5.0,<7.0
+numpy>=1.11,<1.14
+pandas>=0.19,<1.0
+seaborn>=0.7,<0.9
+statsmodels>=0.8,<0.9