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 former partner company which
hasn't had any involvement in the library for many years, and is unlikely to do so at any point in the future. So the
metadata is changed to use the standard value.

Author: per1234

library.properties

@@ -1,10 +1,10 @@
 name=Temboo
 author=Temboo
-maintainer=Temboo <[email protected]>
+maintainer=Arduino <[email protected]>
 sentence=This library enables calls to Temboo, a platform that connects Arduino boards to 100+ APIs, databases, code utilities and more. 
 paragraph=Use this library to connect your Arduino board to Temboo, making it simple to interact with a vast array of web-based resources and services.
 category=Communication
 url=http://www.temboo.com/arduino
 architectures=*
 version=1.2.1
-core-dependencies=arduino (>=1.5.0)
+core-dependencies=arduino (>=1.5.0)