Insert a missing word

This phrase part was missing the «it» word as a subject.

New lines were reorganized a bit in order to respect the 80 character
wrap length.

Author: Fabien Schurter

components/dependency_injection/types.rst

@@ -170,8 +170,8 @@ The disadvantages of setter injection are:
 
 * The setter can be called more than just at the time of construction so
   you cannot be sure the dependency is not replaced during the lifetime of the
-  object (except by explicitly writing the setter method to check if has already been
-  called).
+  object (except by explicitly writing the setter method to check if it has already
+  been called).
 
 * You cannot be sure the setter will be called and so you need to add checks
   that any required dependencies are injected.