boost: Package Version Update -> 1.69.0

boost: Package Version Update -> 1.69.0

This package update provides one new library:
 -> Safe Numerics: A library for guaranteed correct integer arithmetic for
      C++14 and later, from Robert Ramey [1].

Discontinued Libraries
-> Signals (v1) is now removed. Its removal was announced in 1.68 and its
   deprecation was announced in 1.54. Boost 1.68 is the last release that
   provides this library. Users are encouraged to use Signals2 instead.
   The Boost community thanks Douglas Gregor for his work on Signals which
   served its users well and which also inspired Signals2 [2].

More info can be found at the usual place [3].

[1] : https://www.boost.org/doc/libs/1_69_0/libs/safe_numerics/doc/html/index.html
[2] : https://www.boost.org/doc/libs/1_69_0/doc/html/signals2.html
[3] : https://www.boost.org/users/history/version_1_69_0.html

Signed-off-by: Carlos Miguel Ferreira <carlosmf.pt@gmail.com>