Use strings instead of consts for resistor_colours exercise

resistor_colours.lua

@@ -1,18 +1,4 @@
 -- Solution --------------------------------------------------------------------
--- Give the colours whatever values are convenient
-black = undefined
-brown = undefined
-red = undefined
-orange = undefined
-yellow = undefined
-green = undefined
-blue = undefined
-violet = undefined
-grey = undefined
-white = undefined
-gold = undefined
-silver = undefined
-
 function decode_resistance(colours)
 	-- Your implementation here
 end
@@ -22,27 +8,27 @@ end
 local luaunit = require("luaunit.luaunit")
 
 function test_violet_orange_black_is_73_ohms()
-	local resistance = decode_resistance({violet, orange, black})
+	local resistance = decode_resistance({"violet", "orange", "black"})
 	luaunit.assertEquals(resistance, 73)
 end
 
 function test_brown_green_black_is_15_ohms()
-	local resistance = decode_resistance({brown, green, black})
+	local resistance = decode_resistance({"brown", "green", "black"})
 	luaunit.assertEquals(resistance, 15)
 end
 
 function test_green_blue_orange_is_56_kiloohms()
-	local resistance = decode_resistance({green, blue, orange})
+	local resistance = decode_resistance({"green", "blue", "orange"})
 	luaunit.assertEquals(resistance, 56000)
 end
 
 function test_white_yellow_yellow_is_940_kiloohms()
-	local resistance = decode_resistance({white, yellow, yellow})
+	local resistance = decode_resistance({"white", "yellow", "yellow"})
 	luaunit.assertEquals(resistance, 940000)
 end
 
 function test_orange_red_silver_is_320_milliohms()
-	local resistance = decode_resistance({orange, red, silver})
+	local resistance = decode_resistance({"orange", "red", "silver"})
 	luaunit.assertEquals(resistance, 0.32)
 end