Update panic-semihosting version in generated Cargo.toml

[bobgates]

At the moment, cortex-m-quickstart generates a Cargo.toml that includes a dependency on panic-semihosting version 0.3.0

This leads to an error when building:

error[E0557]: feature has been removed
  --> /Users/declan/.cargo/registry/src/github.1485827954.workers.dev-1ecc6299db9ec823/panic-semihosting-0.3.0/src/lib.rs:59:12
   |
59 | #![feature(panic_implementation)]
   |            ^^^^^^^^^^^^^^^^^^^^
   |
note: subsumed by `#[panic_handler]` 

If the version of panic-semihosting is changed to 0.5.2, then the generated program builds as per the instructions in the documentation.