Add details of 20190808 FIPS certification.

Change-Id: I4d17e1e6f24b623ee39a844def8f265eb5e6c6cc
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/42144
Commit-Queue: Adam Langley <alangley@gmail.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

crypto/fipsmodule/FIPS.md

@@ -10,6 +10,7 @@ BoringCrypto has undergone the following validations:
 
 1. 2017-06-15: certificate [#2964](https://csrc.nist.gov/Projects/Cryptographic-Module-Validation-Program/Certificate/2964), [security policy](/crypto/fipsmodule/policydocs/BoringCrypto-Security-Policy-20170615.docx) (in docx format).
 1. 2018-07-30: certificate [#3318](https://csrc.nist.gov/Projects/Cryptographic-Module-Validation-Program/Certificate/3318), [security policy](/crypto/fipsmodule/policydocs/BoringCrypto-Security-Policy-20180730.docx) (in docx format).
+1. 2019-08-08: certificate [#3678](https://csrc.nist.gov/Projects/Cryptographic-Module-Validation-Program/Certificate/3678), [security policy](/crypto/fipsmodule/policydocs/BoringCrypto-Security-Policy-20190808.docx) (in docx format).
 
 ## Running CAVP tests