fix .to.hex() outputting decimal hex values (fixes #25)

Author: Qix-

index.js

@@ -237,6 +237,6 @@ function clamp(num, min, max) {
 }
 
 function hexDouble(num) {
-	var str = num.toString(16).toUpperCase();
+	var str = Math.round(num).toString(16).toUpperCase();
 	return (str.length < 2) ? '0' + str : str;
 }

test/basic.js

@@ -185,3 +185,6 @@ assert.equal(string.to.keyword([100, 255, 0]), undefined);
 // Make sure .get() doesn't return object prototype values (regression test, #44)
 Object.keys(Object.getOwnPropertyDescriptors(Object.prototype))
 	.map(property => assert.deepStrictEqual([property, string.get(property)], [property, null]));
+
+// Make sure writing decimal values as hex doesn't cause bizarre output (regression test, #25)
+assert.equal(string.to.hex([44.2, 83.8, 44]), '#2C542C');