Add extra quotes as per https://github.com/Ultimaker/Cura/pull/1350#discussion_r99554294

resources/definitions/renkforce_rf100.def.json

@@ -58,7 +58,7 @@
             "value": "100"
         },
         "machine_end_gcode": {
-            "value": ";End GCode\nM104 S0 ;extruder heater off\nM140 S0 ;heated bed heater off (if you have it)\nG91 ;relative positioning\nG1 E-1 F300 ;retract the filament a bit before lifting the nozzle, to release some of the pressure\nG1 Z+0.5 E-5 X-20 Y-20 F{speed_travel} ;move Z up a bit and retract filament even more\nG28 X0 Y0 ;move X/Y to min endstops, so the head is out of the way\nM84 ;steppers off\nG90 ;absolute positioning"
+            "value": "';End GCode\nM104 S0 ;extruder heater off\nM140 S0 ;heated bed heater off (if you have it)\nG91 ;relative positioning\nG1 E-1 F300 ;retract the filament a bit before lifting the nozzle, to release some of the pressure\nG1 Z+0.5 E-5 X-20 Y-20 F{speed_travel} ;move Z up a bit and retract filament even more\nG28 X0 Y0 ;move X/Y to min endstops, so the head is out of the way\nM84 ;steppers off\nG90 ;absolute positioning'"
         },
         "machine_gcode_flavor": {
             "value": "RepRap (Marlin/Sprinter)"
@@ -70,7 +70,7 @@
             "value": "Renkforce RF100"
         },
         "machine_start_gcode": {
-            "value": ";Sliced at: {day} {date} {time}\nG21 ;metric values\nG90 ;absolute positioning\nM82 ;set extruder to absolute mode\nM107 ;start with the fan off\nG28 X0 Y0 ;move X/Y to min endstops\nG28 Z0 ;move Z to min endstops\nG1 Z15.0 F{speed_travel} ;move the platform down 15mm\nG92 E0 ;zero the extruded length\nG1 F200 E3 ;extrude 3mm of feed stock\nG92 E0 ;zero the extruded length again\nG1 F{speed_travel}\nM117 Printing..."
+            "value": "';Sliced at: {day} {date} {time}\nG21 ;metric values\nG90 ;absolute positioning\nM82 ;set extruder to absolute mode\nM107 ;start with the fan off\nG28 X0 Y0 ;move X/Y to min endstops\nG28 Z0 ;move Z to min endstops\nG1 Z15.0 F{speed_travel} ;move the platform down 15mm\nG92 E0 ;zero the extruded length\nG1 F200 E3 ;extrude 3mm of feed stock\nG92 E0 ;zero the extruded length again\nG1 F{speed_travel}\nM117 Printing...'"
         },
         "machine_width": {
             "value": "100"