DOC: Note new minimum Numpy

Author: effigies

doc/source/installation.rst

@@ -84,7 +84,7 @@ Requirements
 .. check these against setup.cfg
 
 *  Python_ 3.6 or greater
-*  NumPy_ 1.13 or greater
+*  NumPy_ 1.14 or greater
 *  Packaging_ 14.3 or greater
 *  SciPy_ (optional, for full SPM-ANALYZE support)
 *  h5py_ (optional, for MINC2 support)