Compilation fails because of an outdated version of pbr

[mattbasta]

PBR fails to compile when building zrtstr due to this error:

error[E0283]: type annotations required: cannot resolve `std::string::String: std::convert::AsRef<_>`
   --> /Users/basta/.cargo/git/checkouts/pb-06f1c94bfc11587f/a1bf8ce/src/pb.rs:334:68
    |
334 |                             base = base + repeat!(self.bar_current.as_ref(), curr_count - 1) +
    |                                           -------------------------^^^^^^------------------- in this macro invocation

error: aborting due to previous error

Upgrading PBR to the latest version fixes the problem entirely. I don't know Rust well enough to contribute a proper fix, but fiddling with the PBR version and regenerating the Cargo.lock file made the compilation process succeed without any problems, and the tool works as expected.