Set gitmodules to merge upon update.

See https://stackoverflow.com/a/55570998/1878788

This will need to be done also when new submodules are added.

.gitmodules

 [submodule "qaf_demux"]
 	path = qaf_demux
 	url = https://bioinfo_utils:KU13FfM3kLyeCrWpD2ZG@gitlab.pasteur.fr/bli/qaf_demux.git
+	update = merge
 [submodule "libcelegans"]
 	path = libcelegans
 	url = https://bioinfo_utils:izoZHUvhFJU8689hqM5u@gitlab.pasteur.fr/bli/libcelegans.git
+	update = merge
 [submodule "libworkflows"]
 	path = libworkflows
 	url = https://bioinfo_utils:tfuTQsSZWMtC5xXJNFJh@gitlab.pasteur.fr/bli/libworkflows.git
+	update = merge
 [submodule "libhts"]
 	path = libhts
 	url = https://bioinfo_utils:DP-sqNot8AdsMek_KJiC@gitlab.pasteur.fr/bli/libhts.git
+	update = merge
 [submodule "libdeseq"]
 	path = libdeseq
 	url = https://bioinfo_utils:uqiFbzWyBtzxYn7br82P@gitlab.pasteur.fr/bli/libdeseq.git
+	update = merge
 [submodule "libsmallrna"]
 	path = libsmallrna
 	url = https://bioinfo_utils:FjgTxcUGPsGVQ-yZZVyS@gitlab.pasteur.fr/bli/libsmallrna.git
+	update = merge
 [submodule "plotting_scripts"]
 	path = plotting_scripts
 	url = https://bioinfo_utils:S7FAyfgzBnvGq_MtWLkz@gitlab.pasteur.fr/bli/plotting_scripts.git
+	update = merge
 [submodule "snakemake_wrappers"]
 	path = snakemake_wrappers
 	url = https://bioinfo_utils:Ues9rP1tyfzs1zs5BzpY@gitlab.pasteur.fr/bli/snakemake_wrappers.git
+	update = merge
 [submodule "bam25prime"]
 	path = bam25prime
 	url = https://bioinfo_utils:UTSWyWVPdw_kbxWR7-zD@gitlab.pasteur.fr/bli/bam25prime.git
+	update = merge