Fix add_num_to_string not printing 10

examples/loops.reid

@@ -6,7 +6,7 @@ import std::add_num_to_str;
 import std::free_string;
 
 fn main() -> u32 {
-  for i in 0 .. 5 {
+  for i in 0 .. 15 {
     let mut text = new_string();
     add_num_to_str(&mut text, i);
     print(&text);

reid/lib/std.reid

@@ -93,7 +93,7 @@ fn str_length(string: *char, position: u32) -> u32 {
 }
 
 pub fn add_num_to_str(string: &mut String, num: u64) {
-    if num > 10 {
+    if num >= 10 {
         add_num_to_str(string, num / 10)
     }
     let rem = num % 10;