TensorFlow 1.15.1 release, fix security vulnerabilities

TensorFlow 1.15.1 release, this is a security update release.

This version updates are as follows:

• Fixes a security vulnerability, which Python string into tf.float16 value produces a segmentation fault ( CVE-2020-5215 )
• curl upgrade to 7.66.0 to address  CVE-2019-5482  and  CVE-2019-5481
• sqlite3 upgrade to 3.30.01 to address  CVE-2019-19646 , CVE-2019-19645  and  CVE-2019-16168

Release Notes:

https://github.com/tensorflow/tensorflow/releases/tag/v1.15.1