Don't use absolute path in #include directive

The `Eigen` library is included by it's full (absolute) path
https://github.com/Baradun/lomov/blob/44db5cc2dc4f6bf5308a01104ac676ba26d281c0/main/main.cpp#L9
this is uncommon and very system-dependent. Try simple
```
#include <Eigen/Dense>
```
and if that doesn't work update `Makefile` or your build tool to pass path to the "include" directory like
```
g++ ... -I /usr/include/eigen3
```