Fix typo

Dockerfile

@@ -57,7 +57,7 @@ RUN createrepo ${EOSREPODIR}; \
 # as dependency the xrdcp program is in /opt/eos/xrootd/bin/xrdcp and the
 # xrootd-client package is no longer installed and therefore starting the FSTs
 # fails. This only happens on CC7.
-RUN yum install -y --nogpgp install xrootd-client
+RUN yum install -y --nogpg install xrootd-client
 
 # Generate a new forwardable keytab 'eos-test+' to replace the not-forwardable
 # one (installed by the eos-testkeytab package).