Renamed MYSQL_HAS_SHA256

TODO.txt

@@ -2,7 +2,6 @@ Sanitize
 	Valgrindize
 		Use -DBOOST_MYSQL_VALGRIND_TESTS in the appropriate CIs
 		Refactor CMake
-		Rename env variables MYSQL_SHA256 in CIs
 	Bad serialize(value.value) somewhere
 	Copy operations for handshake
 	Test zero dates

ci/build_unix.sh

@@ -14,7 +14,7 @@ if [ $TRAVIS_OS_NAME == "osx" ]; then
 	if [ $DATABASE == "mariadb" ]; then
 		sudo mysql -u root < ci/root_user_setup.sql
 	else
-		export MYSQL_HAS_SHA256=1
+		export BOOST_MYSQL_HAS_SHA256=1
 	fi
 else
 	sudo cp ci/unix-ci.cnf /etc/mysql/conf.d/