Bump LT version numbers

We're adding the ambisonics API
diff --git a/configure.ac b/configure.ac
index 02f0939..e2921fa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -22,9 +22,9 @@
 
 # For libtool.
 dnl Please update these for releases.
-OPUS_LT_CURRENT=6
-OPUS_LT_REVISION=1
-OPUS_LT_AGE=6
+OPUS_LT_CURRENT=7
+OPUS_LT_REVISION=0
+OPUS_LT_AGE=7
 
 AC_SUBST(OPUS_LT_CURRENT)
 AC_SUBST(OPUS_LT_REVISION)