fix(wording): fix on title syntax

Author: Guikingone

service_container/injection_types.rst

@@ -101,7 +101,7 @@ combination with class hierarchies: if a class uses constructor injection
 then extending it and overriding the constructor becomes problematic.
 
 Immutable-setter Injection
--------------------
+--------------------------
 
 Another possible injection in to use a method which return ``static``,
 this approach allow you to make a service immutable::