[RFR] Pin numpy to 1.15.4

Workaround for
pandas-dev#27435

Author: StefanRijnhart

requirements-dev.txt

@@ -1,4 +1,4 @@
-numpy>=1.15
+numpy==1.15.4
 python-dateutil>=2.5.0
 pytz
 asv
@@ -43,4 +43,4 @@ xarray
 xlrd
 xlsxwriter
 xlwt
-cpplint
+cpplint

setup.py

@@ -30,14 +30,14 @@ def is_platform_mac():
     return sys.platform == 'darwin'
 
 
-min_numpy_ver = '1.12.0'
+min_numpy_ver = '1.15.4'
 setuptools_kwargs = {
     'install_requires': [
         'python-dateutil >= 2.5.0',
         'pytz >= 2011k',
-        'numpy >= {numpy_ver}'.format(numpy_ver=min_numpy_ver),
+        'numpy = {numpy_ver}'.format(numpy_ver=min_numpy_ver),
     ],
-    'setup_requires': ['numpy >= {numpy_ver}'.format(numpy_ver=min_numpy_ver)],
+    'setup_requires': ['numpy = {numpy_ver}'.format(numpy_ver=min_numpy_ver)],
     'zip_safe': False,
 }