Make proton diameter more consistent with experimental results

presets/objects.js

@@ -428,7 +428,7 @@ function makeObjects() {
                     rename: true
                 },
                 proton: {
-                    height: math.unit(1e-15, "m"),
+                    height: math.unit(0.877e-15, "m"),
                     mass: math.unit(1, "dalton"),
                     image: { source: "./media/objects/circle.svg" },
                     name: "Proton",