MAINT: Fixes to requirements

requirements-dev.txt

@@ -4,4 +4,4 @@ mock==2.*
 coverage==4.*
 pytest==3.*
 pytest-cov==2.*
-pytest-runner>=2,<=3
+pytest-runner>=2.*,<=4.*

requirements-extra.txt

 indexed_gzip>=0.7.0,<1
 wxpython>=3.0.2.0,<4.1
 trimesh>=2.22.28,<3
-rtree==0.8
+rtree==0.8.3

requirements.txt

 six==1.*
-deprecation>=1,<=2
+deprecation>=1.*,<=2.*
 numpy==1.*
 scipy>=0.18,<2
 nibabel==2.*