cargo build with rust-1.37 has warnings: trait objects without an explicit `dyn` are deprecated

[stefson]

for the moment it's only a warning, but it might be turned into an error in the future.

here's the full build log:

cargo build
  Downloaded error-chain v0.7.2
  Downloaded toml v0.2.1
  Downloaded rustc_version v0.1.7
  Downloaded cargo_metadata v0.5.8
  Downloaded semver v0.1.20
  Downloaded walkdir v1.0.7
  Downloaded same-file v0.1.3
   Compiling proc-macro2 v1.0.3
   Compiling unicode-xid v0.2.0
   Compiling syn v1.0.5
   Compiling libc v0.2.62
   Compiling ryu v1.0.0
   Compiling serde v1.0.100
   Compiling itoa v0.4.4
   Compiling semver-parser v0.7.0
   Compiling remove_dir_all v0.5.2
   Compiling cargo-xbuild v0.5.16 (/tmp/cargo-xbuild)
   Compiling error-chain v0.11.0
   Compiling semver v0.1.20
   Compiling same-file v0.1.3
   Compiling rustc-serialize v0.3.24
   Compiling error-chain v0.7.2
   Compiling walkdir v1.0.7
   Compiling rustc_version v0.1.7
   Compiling quote v1.0.2
   Compiling rand v0.4.6
   Compiling fs2 v0.4.3
   Compiling toml v0.2.1
   Compiling tempdir v0.3.7
   Compiling serde_derive v1.0.100
   Compiling serde_json v1.0.40
   Compiling semver v0.9.0
   Compiling cargo_metadata v0.5.8
warning: trait objects without an explicit `dyn` are deprecated
   --> src/flock.rs:139:11
    |
139 |     try: &Fn() -> io::Result<()>,
    |           ^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn() -> io::Result<()>`

warning: trait objects without an explicit `dyn` are deprecated
   --> src/flock.rs:140:13
    |
140 |     block: &Fn() -> io::Result<()>,
    |             ^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Fn() -> io::Result<()>`

    Finished dev [unoptimized + debuginfo] target(s) in 25.92s
´´´

[phil-opp]

Thanks for reporting! Fix in #46.