Changelog: Add entry for prime test improvement
mbed TLS ChangeLog (Sorted per branch, date)
+= mbed TLS x.x.x branch released xxxx-xx-xx
+
+Changes
+ * Add MBEDTLS_MPI_GEN_PRIME_FLAG_LOW_ERR flag to mbedtls_mpi_gen_prime() and
+ use it to reduce error probability in RSA key generation to levels mandated
+ by FIPS-186-4.
+
= mbed TLS 2.13.1 branch released 2018-09-06
API Changes
