Fix links to package administration doc

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

doc/administration/maven_repository.md

@@ -16,4 +16,4 @@ Once enabled, newly created projects will have the Packages feature enabled by
 default. Existing projects will need to
 [explicitly enabled it](../user/project/packages/maven_repository.md#enabling-the-packages-repository).
 
-To enable the Maven repository you need to enable [Packages feature](./packages.md)
+To enable the Maven repository you need to enable [Packages feature](packages.md)

doc/administration/npm_registry.md

@@ -16,4 +16,4 @@ Once enabled, newly created projects will have the Packages feature enabled by
 default. Existing projects will need to
 [explicitly enabled it](../user/project/packages/npm_registry.md#enabling-the-packages-repository).
 
-To enable the NPM Registry you need to enable [Packages feature](./packages.md)
+To enable the NPM Registry you need to enable [Packages feature](packages.md)

doc/administration/packages.md

@@ -2,8 +2,8 @@
 
 Package feature provides a support for next products:
 
-* [Maven Repository](./maven_repository)
-* [NPM Registry](./npm_registry)
+* [Maven Repository](maven_repository.md)
+* [NPM Registry](npm_registry.md)
 
 ## Enabling the Packages feature