crates_vendor doesn't support build metadata in version strings

[granaghan]

In my Cargo.toml, I have:

proc-macro-hack = "0.5.20+deprecated"

crates_vendor downloads the crate into proc-macro-hack-0.5.20+deprecated, however the generated rules replace the "+" with a "-", causing errors.

alias(                                                                                                                                                                                                                                                                         
    name = "proc-macro-hack",                                                                                                                                                                                                                                                  
    actual = "//third_party/cargo/registry/bazel/no_std/vendor/proc-macro-hack-0.5.20-deprecated:proc_macro_hack",                                                                                                                                                             
    tags = ["manual"],                                                                                                                                                                                                                                                         
)