Fix wrong error message when updating map for non exist key

larrylv · José Valim · commit eec6d3900076 · 2016-01-03T09:54:59.000+01:00
``` elixir
iex(7)&gt; map = %{:a =&gt; 1, 2 =&gt; :b}
%{2 =&gt; :b, :a =&gt; 1}
iex(8)&gt; %{map | :c =&gt; 3}
** (KeyError) key :c not found in: %{2 =&gt; :b, :a =&gt; 1}
```
diff --git a/getting-started/maps-and-dicts.markdown b/getting-started/maps-and-dicts.markdown
@@ -185,7 +185,7 @@ iex> map.c
 iex> %{map | :a => 2}
 %{:a => 2, 2 => :b}
 iex> %{map | :c => 3}
-** (ArgumentError) argument error
+** (KeyError) key :c not found in: %{2 => :b, :a => 1}
 ```
 
 Both access and update syntaxes above require the given keys to exist. For example, accessing and updating the `:c` key failed because there is no `:c` in the map.
