[PATCH] Add missing option "--pattern" to svndumpfilter bash_completion script

This was reported at https://svn.haxx.se/users/archive-2017-09/0040.shtml
with some poorly formatted answer from myself.

Anyhow...

It seems the svndumpfilter option --pattern was missing
from the bash_completion script, so i updated mine
and it seems to work nice.

This is my first bug report and (very trivial) patch,
please be kind :-)

How to reproduce ( not C&P ) since you have to TAB for the completion to
take place.

ycdtosa_at_debian9:~/subversion/svn-trunk$ svndumpfilter include --[TAB]
> --drop-empty-revs --preserve-revprops
> --renumber-revs --targets
> --help --quiet
> --skip-missing-merge-sources
>

as you can see, --pattern does not show up.

[[[
      Add the missing --pattern option
      to svndumpfilter bash completion
      for the exclude and include operations
]]]

Thanks in advance.