[haxe/en] Fix typo (#2756)

- [x] I solemnly swear that this is all original content of which I am the original author
- [x] Pull request title is prepended with `[language/lang-code]`
- [x] Pull request touches only one file (or a set of logically related files with similar changes made)
- [x] Content changes are aimed at *intermediate to experienced programmers* (this is a poor format for explaining fundamental programming concepts)
- [x] If you've changed any part of the YAML Frontmatter, make sure it is formatted according to [CONTRIBUTING.md](https://github.com/adambard/learnxinyminutes-docs/blob/master/CONTRIBUTING.markdown)
  - [x] Yes, I have double-checked quotes and field names!

Output:
My dog's name isfido, and his other favorite thing is a: teddy

New output:
My dog's name is fido, and his other favorite thing is a: teddy

haxe.html.markdown

@@ -380,7 +380,7 @@ class LearnHaxe3{
         // The "_" case above is a "wildcard" value
         // that will match anything.
 
-        trace("My dog's name is" + my_dog_name
+        trace("My dog's name is " + my_dog_name
                 + ", and his favorite thing is a: "
                 + favorite_thing);
 
@@ -406,7 +406,7 @@ class LearnHaxe3{
             default     : "some unknown treat";
         }
 
-        trace("My dog's name is" + my_dog_name
+        trace("My dog's name is " + my_dog_name
                 + ", and his other favorite thing is a: "
                 + other_favorite_thing);