DOC fix links in install section

doc/installing.rst

@@ -9,7 +9,7 @@ Required dependencies
 - Python 3.5 or later.
 - `numpy <http://www.numpy.org/>`__
 - `xarray <http://xarray.pydata.org>`__ (0.10.0 or later)
-- `numba <http://numba.pydata.org/>`__ (0.29.0 or later)
+- `numba <http://numba.pydata.org/>`__ (0.35.0 or later)
 
 Optional dependencies
 ---------------------
@@ -68,10 +68,6 @@ For development purpose, use the following command::
 
     $ pip install -e .
 
-.. _PyPi: https://pypi.python.org/pypi
-.. _conda-forge: https://conda-forge.github.io/
-.. _conda: http://conda.io/
-
 Import xarray-topo
 ------------------