Change libtool c:r:a from 4:0:1 to 4:1:1

Update libtool c:r:a for the libaom 3.1.1 release. The last public
release is libaom 3.1.0, which has current=4, revision=0, age=1.

The six rules in libtool.html#Updating-version-info are applied as
follows:
  Rule 1: N/A
  Rule 2: N/A
  Rule 3: Yes, so increment revision from 0 to 1.
  Rule 4: No.
  Rule 5: No.
  Rule 6: No.

The net change is: bump revision only, don’t touch current nor age.

BUG=aomedia:3056

Change-Id: Id902e42e415c7df1588b3e7702b34685270cdb64

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ee64fc0..9b37498 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -43,7 +43,7 @@
 #
 # We set SO_FILE_VERSION = [c-a].a.r
 set(LT_CURRENT 4)
-set(LT_REVISION 0)
+set(LT_REVISION 1)
 set(LT_AGE 1)
 math(EXPR SO_VERSION "${LT_CURRENT} - ${LT_AGE}")
 set(SO_FILE_VERSION "${SO_VERSION}.${LT_AGE}.${LT_REVISION}")