Use standardized maintainer metadata property value

The `maintainer` property of the library.properties metadata file defines the entity responsible for maintenance of the
library.

In the libraries that are under Arduino's maintainership, it is standard practice to set the `maintainer` property to
the general purpose value "Arduino <[email protected]>".

Previously, instead of that standard value, this library's `maintainer` property defined a specific Arduino team member
as the maintainer. This is prone to "bit rot", as the scope of each individual's work may change over time, or they may
even move on from working for Arduino. It is unlikely that the team member will remember to update the metadata values
at such time as they are no longer able to dedicate themselves to maintaining the library. So the metadata is changed to
use the standard value.

It is commendable for individual team members to take responsibility for maintenance of specific libraries. However,
doing so is not in any way dependent on the value of a metadata property. The change to the metadata does not imply any
change to maintenance responsibilities for the project.

Author: per1234

library.properties

@@ -1,7 +1,7 @@
 name=Arduino_Opta_Blueprint
 version=0.2.6
 author=Daniele Aimo ([email protected])
-maintainer=Daniele Aimo (d.aimo@arduino.cc)
+maintainer=Arduino <info@arduino.cc>
 sentence=Library used to connect OPTA and OPTA Expansion Modules on I2C / UART 
 paragraph=This library discover the presence of different Expansions (for example OPTA Digital) present on the I2C bus, automatically assing addresses to them and allow to control their Input/Output from the Opta Controller.
 category=Communication