Use `#send` in `.install_proxy_methods`

# Why?
Old approach would raise a syntax error in the for
`method_missing`/`.install_proxy_methods` for such assignment methods.

# What?
In order to proxy syntactic sugar methods (e.g. some_attribute=), use `#send`
in the module_eval.  

# FOSS notes
Want to field test this change with our project before making a PR upstream.