[Bug-gsl]typo in documentation

[Martin Jansche]

Hi Brian et al.,

There is[1] a typo in doc/specfunc-gamma.texi in the description of
gsl_sf_poch().  Formula

  @math{(a)_x := \Gamma(a + x)/\Gamma(x)}

should be replaced with

  @math{(a)_x := \Gamma(a + x)/\Gamma(a)}

- martin

[1] Connections to sources.redhat.com are timing out, so I may not
have the latest CVS revisions.