Wrap PixhawkInstruction values in float()

[benjaminwp18]

PixhawkInstruction values must be floats. Python is weird, so computed values should be passed through the float() function before being passed to PixhawkInstruction(). i.e.

PixhawkInstruction(
    forward=float(0.5),
    vertical=float(-0.25),
    author=PixhawkInstruction.MANUAL_CONTROL
)

Write instructions to that effect.