Update version to 2.7.5

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index 6cdb840..c75c74c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,6 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
-= mbed TLS x.x.x branch released xxxx-xx-xx
+= mbed TLS 2.7.5 branch released 2018-07-25
 
 Security
    * Fix a vulnerability in TLS ciphersuites based on CBC and using SHA-384,