Update Slf4j to 1.7.21
Update Slf4j to 1.7.21

openam-org-ru/org.jsmpp,amdtelecom/jsmpp,openam-org-ru/org.jsmpp,pmoerenhout/jsmpp-1,opentelecoms-org/jsmpp,amdtelecom/jsmpp,opentelecoms-org/jsmpp,pmoerenhout/jsmpp-1