build(cargo): add alias to upgrade gva-conf

.cargo/config

@@ -7,4 +7,5 @@ ta = "test --all"
 rr = "run --release --"
 uc = "update -p duniter-core"
 ug = "update -p duniter-gva"
+ugc = "update -p duniter-gva-conf"
 xtask = "run --package xtask --"