upgrade bouncycastle library to latest version

[namtruong]

update bouncycastle library to latest version which contains a fix for vulnerability CVE-2018-1000613.
More details at https://nvd.nist.gov/vuln/detail/CVE-2018-1000613

[codecov-io]

Codecov Report

Merging #686 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #686   +/-   ##
=========================================
  Coverage     99.49%   99.49%           
  Complexity     1859     1859           
=========================================
  Files           285      285           
  Lines          5545     5545           
  Branches        278      278           
=========================================
  Hits           5517     5517           
  Misses            5        5           
  Partials         23       23

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