Fix the Falco version

[leodido]

Describe the bug

Currently, when Falco builds, the cmake computes its version looking at the git index.

At the moment, cmake outputs version with an unwanted leading 0.

How to reproduce it

mkdir -p build
cd build
cmake ..

Look at the cmake output.

Expected behaviour

...
-- Falco version: 0.19.0+e1a753f
...

Screenshots

...
-- Falco version: 0.0.19.0+e1a753f
...

[leodido]

/assign