Update travis to handle custom_bootscreen.h files

buildroot/bin/restore_configs

@@ -3,3 +3,7 @@
 cp Marlin/Configuration.h.backup      Marlin/Configuration.h
 cp Marlin/Configuration_adv.h.backup  Marlin/Configuration_adv.h
 cp Marlin/pins_RAMPS_14.h.backup      Marlin/pins_RAMPS_14.h
+
+if [ -f Marlin/_Bootscreen.h ]; then
+  rm Marlin/_Bootscreen.h
+fi

buildroot/bin/use_example_configs

@@ -1,3 +1,7 @@
 #!/usr/bin/env bash
 
-eval "cp Marlin/example_configurations/$1/Configuration* Marlin/"
+eval "cp Marlin/example_configurations/${1}/Configuration* Marlin/"
+
+if [ -f "Marlin/example_configurations/${1}/_Bootscreen.h" ]; then
+  cp "Marlin/example_configurations/${1}/_Bootscreen.h" Marlin/
+fi