Remove version specfic links (#742)

* Fixes to concept tree

* Update links to point to the latest Crystal documentation

Author: meatball133

concepts/conditionals/links.json

@@ -8,7 +8,7 @@
     "description": "Crystal docs: Unless"
   },
   {
-    "url": "https://crystal-lang.org/reference/1.8/syntax_and_semantics/as_a_suffix.html",
+    "url": "https://crystal-lang.org/reference/latest/syntax_and_semantics/as_a_suffix.html",
     "description": "Crystal docs: If as suffix"
   },
   {

concepts/iteration/links.json

@@ -8,7 +8,7 @@
     "description": "Crystal docs: Unless"
   },
   {
-    "url": "https://crystal-lang.org/reference/1.8/syntax_and_semantics/as_a_suffix.html",
+    "url": "https://crystal-lang.org/reference/latest/syntax_and_semantics/as_a_suffix.html",
     "description": "Crystal docs: If as suffix"
   },
   {

exercises/practice/complex-numbers/.docs/instructions.append.md

@@ -1,4 +1,4 @@
 In this exercise you will need to add methods to an existing struct (`Number`).
 You can see an example of this in the Crystal documentation for [getters and setters][getters-and-setters]
 
-[getters-and-setters]: https://crystal-lang.org/reference/1.9/syntax_and_semantics/methods_and_instance_variables.html#getters-and-setters
+[getters-and-setters]: https://crystal-lang.org/reference/latest/syntax_and_semantics/methods_and_instance_variables.html#getters-and-setters

exercises/practice/state-of-tic-tac-toe/.docs/instructions.append.md

@@ -5,4 +5,4 @@ You can read more about enums and unions in the Crystal reference documentation:
 - [union][union]
 
 [enum]: https://crystal-lang.org/reference/latest/syntax_and_semantics/enum.html
-[union]: https://crystal-lang.org/reference/1.8/syntax_and_semantics/union_types.html
+[union]: https://crystal-lang.org/reference/latest/syntax_and_semantics/union_types.html