tomahawk: Pin boost to version 1.55

The dependency of boost propagated by Lucene++ is version 1.55, so this
leads to a segfault during startup because we get mixed library versions
with boost 1.62 and 1.55 in the binary.

I've tested running Tomahawk before and after this change and the change
indeed fixes the problem.

Signed-off-by: aszlig <aszlig@nix.build>
Fixes: #17598, #19238