Update the ABI version to 1:0:0

As per the [libtool versioning guidelines][1].

>If any interfaces have been added, removed, or changed since the
>last update, increment current, and set revision to 0.

[1]: https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html

Author: xzyfer

src/GNUmakefile.am

@@ -34,7 +34,7 @@ include $(top_srcdir)/Makefile.conf
 
 libsass_la_SOURCES = ${CSOURCES} ${SOURCES}
 
-libsass_la_LDFLAGS = $(AM_LDFLAGS) -no-undefined -version-info 0:9:0
+libsass_la_LDFLAGS = $(AM_LDFLAGS) -no-undefined -version-info 1:0:0
 
 if ENABLE_TESTS
 if ENABLE_COVERAGE