Release 1.15.2

Note that this release no longer has a single pip package for GPU and CPU. Please see #36347 for history and details

Bug Fixes and Other Changes

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