Update .gitignore

Deleted kuben-B_Cu.svg, kuben-F_Cu.svg, kuben.kicad_pcb-bak, kuben.sch-bak files

.gitignore

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+# For PCBs designed using KiCad: http://www.kicad-pcb.org/
+# Format documentation: http://kicad-pcb.org/help/file-formats/
+
+# Temporary files
+*.000
+*.bak
+*.bck
+*.kicad_pcb-bak
+*~
+_autosave-*
+*.tmp
+*-rescue.lib
+*-save.pro
+*-save.kicad_pcb
+
+# Netlist files (exported from Eeschema)
+*.net
+
+# Autorouter files (exported from Pcbnew)
+*.dsn
+*.ses
+
+# Exported BOM files
+*.xml
+*.csv