Log Message:
expat: update to 2.2.7.

For a security fix.

Release 2.2.7 Wed June 19 2019
        Security fixes:
       #186 #262  Fix extraction of namespace prefixes from XML names;
                    XML names with multiple colons could end up in the
                    wrong namespace, and take a high amount of RAM and CPU
                    resources while processing, opening the door to
                    use for denial-of-service attacks

        Other changes:
       #195 #197  Autotools/CMake: Utilize -fvisibility=hidden to stop
                    exporting non-API symbols
            #227  Autotools: Add --without-examples and --without-tests
            #228  Autotools: Modernize configure.ac
       #245 #246  Autotools: Fix check for -fvisibility=hidden for Clang
       #247 #248  Autotools: Fix compilation for lack of docbook2x-man
       #236 #258  Autotools: Produce .tar.{gz,lz,xz} release archives
            #212  CMake: Make libdir of pkgconfig expat.pc support multilib
       #158 #263  CMake: Build man page in PROJECT_BINARY_DIR not _SOURCE_DIR
            #219  Remove fallback to bcopy, assume that memmove(3) exists
            #257  Use portable "/usr/bin/env bash" shebang (e.g. for \ 
OpenBSD)
            #243  Windows: Fix syntax of .def module definition files
                  Version info bumped from 7:8:6 to 7:9:6

        Special thanks to:
            Benjamin Peterson
            Caolán McNamara
            Hanno Böck
            KangLin
            Kishore Kunche
            Marco Maggi
            Rhodri James
            Sebastian Dröge
            userwithuid
            Yury Gribov