[Yaml] update changelog and upgrade files

UPGRADE-3.2.md

@@ -70,3 +70,9 @@ Validator
        // ...
    }
    ```
+
+Yaml
+----
+
+ * Mappings with a colon that is not followed by a space are deprecated and
+   will lead to a `ParseException` in Symfony 4.0.

UPGRADE-4.0.md

@@ -147,6 +147,9 @@ Translation
 Yaml
 ----
 
+ * Mappings with a colon that is not followed by a space are are not
+   supported anymore and lead to a `ParseException`.
+
  * Starting an unquoted string with `%` leads to a `ParseException`.
 
  * The `Dumper::setIndentation()` method was removed. Pass the indentation

src/Symfony/Component/Yaml/CHANGELOG.md

@@ -4,6 +4,9 @@ CHANGELOG
 3.2.0
 -----
 
+ * Mappings with a colon that is not followed by a space are deprecated and
+   will lead to a `ParseException` in Symfony 4.0.
+
  * Added support for parsing PHP constants:
 
    ```php