Update library version to 1.3.18

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index f23aee6..d4cf85b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,6 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
-= mbed TLS 1.3.x branch 2016-xx-xx
+= mbed TLS 1.3.18 branch 2016-10-17
 
 Security
    * Removed the MBEDTLS_SSL_AEAD_RANDOM_IV option, because it was not compliant