fix non-integer index error

[grlee77]

This is a fix for the failure on Appveyor in the most recent commit (due to a non-integer shape in the data readers):

FAIL: Doctest: pywt.data._readers.nino
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\python27\lib\doctest.py", line 2226, in runTest
    raise self.failureException(self.format_failure(new.getvalue()))
AssertionError: Failed doctest test for pywt.data._readers.nino
  File "C:\projects\pywt\build\lib\pywt\data\_readers.py", line 142, in nino
----------------------------------------------------------------------
File "C:\projects\pywt\build\lib\pywt\data\_readers.py", line 164, in pywt.data._readers.nino
Failed example:
    time, sst = pywt.data.nino()
Exception raised:
    Traceback (most recent call last):
      File "c:\python27\lib\doctest.py", line 1315, in __run
        compileflags, 1) in test.globs
      File "<doctest pywt.data._readers.nino[1]>", line 1, in <module>
        time, sst = pywt.data.nino()
      File "C:\projects\pywt\build\lib\pywt\data\_readers.py", line 180, in nino
        sst = np.mean(np.reshape(np.array(sst_csv)[:n,4],(n/3,-1)),axis=1)
    TypeError: slice indices must be integers or None or have an __index__ method
----------------------------------------------------------------------
File "C:\projects\pywt\build\lib\pywt\data\_readers.py", line 165, in pywt.data._readers.nino

[grlee77]

The failure started occuring because Appveyor is now using numpy 1.12 which no longer allows floats as indices

[codecov-io]

Current coverage is 86.28% (diff: 100%)

Merging #273 into master will not change coverage

@@             master       #273   diff @@
==========================================
  Files            20         20          
  Lines          3056       3056          
  Methods          45         45          
  Messages          0          0          
  Branches        525        525          
==========================================
  Hits           2637       2637          
  Misses          369        369          
  Partials         50         50          

Powered by Codecov. Last update 47f50e7...bf09301

[grlee77]

went ahead and self-merged this small fix for numpy 1.12 compatibility so that master passes CI again

[rgommers]

thanks!