crates_vendor doesn't support build metadata in version strings

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"],
)
```