Fix link (#729)

Author: dahbka-lis

BUILD.md

@@ -7,7 +7,7 @@ This document has detailed instructions on how to build ydb-python-sdk from sour
 - Install [Docker](https://docs.docker.com/engine/install/).
 - Install [Python](https://docs.python.org/3.8/)
 - Install [pip](https://pip.pypa.io/en/latest/installation/)
-- Install [Tox](https://tox.wiki/en/latest/install.html)
+- Install [Tox](https://tox.wiki/en/latest/installation.html)
 
 ### Clone the repository