Fix typo

Fix typo in ChangeLog entry.
diff --git a/ChangeLog b/ChangeLog
index b7946c3..b50d223 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,7 +3,7 @@
 = mbed TLS x.x.x branch released xxxx-xx-xx
 
 Bugfix
-    * Fix efailure in hmac_drbg in the benchmark sample application, when
+    * Fix failure in hmac_drbg in the benchmark sample application, when
      MBEDTLS_THREADING_C is defined. Found by TrinityTonic, #1095
 
 = mbed TLS 2.1.14 branch released 2018-07-25