Update pull_refresh_strings.xml

Hey Chris! I suggest to update Russian strings. I think, that I need explicite this changes:
1. phrases are shortened to one word, this will improve versatility of translation in apps. it also facilitates reading.
2. phrases begin with a lowercase letter - to improve the typography and reduce the emphasis in GUI, so as not to catch the focus of attention
3. i propose to give up the dots (...) at the end of sentences, to improve the typography - and to preserve the symmetry of the messages on the screen (the alignment of the text).

Сhanges have been tested on a small group of users (about 200) for testing modification program K-9 Mail. proposed changes quite naturally consistent with the rest of the interface.

Thank you in advance for any comments!