fix material icons with underscores (#767)

when they get imported into iconify, they get translated to hyphens,
just like f7

Signed-off-by: Cody Cutrer <cody@cutrer.us>
Co-authored-by: Dan Cunningham <dan@digitaldan.com>

OpenHABCore/Sources/OpenHABCore/Util/Endpoint.swift

@@ -177,6 +177,7 @@ public extension Endpoint {
                 }
                 if source == "material" {
                     source = "iconify"
+                    icon = icon.replacingOccurrences(of: "_", with: "-")
                     icon = "\(set)-\(icon)"
                     set = "ic"
                 }