Update libtool version numbers for libsigrokdecode.

The last release of libsigrokdecode (package version number 0.1.0) had the
initial libtool version numbers (current:revision:age) of 0:0:0.

The upcoming release (0.1.1) is API-compatible with 0.1.0 and can be used
as drop-in replacement. Programs linked against 0.1.0 do not need to
be recompiled or relinked.

As per the libtool guidelines this release only increments the
libtool "revision" number. The new libtool version numbers
(current:revision:age) are thus 0:1:0.

See here for details:
http://www.gnu.org/software/libtool/manual/libtool.html#Updating-version-info