Set SONAME to 6.

Suggested by Stefano Rivera and endorsed by Evangelos Foutras in
dicussion on the GitHub issue, 6 is considered to be larger than
what any distribution is currently using.

Fixes #243.

Change-Id: I92185ccd3109123a3ed3e55693f475a74bc2a9b2
Reviewed-on: https://code-review.googlesource.com/c/re2/+/52738
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/Makefile b/Makefile
index d0107ed..fd9cec6 100644
--- a/Makefile
+++ b/Makefile
@@ -44,7 +44,7 @@
 
 # ABI version
 # http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html
-SONAME=1
+SONAME=6
 
 # To rebuild the Tables generated by Perl and Python scripts (requires Internet
 # access for Unicode data), uncomment the following line: