Update sccache to 0.2.15 to fix ubuntu-latest builds on CI

[phiggins]

No description provided.

[phiggins]

The issue is that running cargo clippy with sccache does not currently work on ubuntu-latest (the mac build gets killed after ubuntu-latest fails, so I don't know its status). The full output of the script/ci step is:

+ source ./script/functions.sh
+++ git rev-parse --show-toplevel
++ REPO_BASE=/home/runner/work/rubyfmt/rubyfmt
+ rm -rf tmp/
+ git submodule init
+ git submodule update
+ make lint
cargo clippy && cd librubyfmt && cargo clippy
   Compiling autocfg v1.0.0
   Compiling libc v0.2.71
   Compiling proc-macro2 v1.0.18
   Compiling unicode-xid v0.2.1
   Compiling syn v1.0.33
   Compiling cc v1.0.55
   Compiling serde_derive v1.0.114
   Compiling fs_extra v1.1.0
   Compiling serde v1.0.114
    Checking cfg-if v0.1.10
   Compiling ryu v1.0.5
   Compiling log v0.4.8
    Checking adler32 v1.1.0
   Compiling serde_json v1.0.55
    Checking gimli v0.21.0
    Checking itoa v0.4.6
    Checking rustc-demangle v0.1.16
    Checking termcolor v1.1.0
    Checking object v0.20.0
    Checking bytecount v0.6.0
   Compiling rubyfmt-main v0.1.0 (/home/runner/work/rubyfmt/rubyfmt)
error: failed to execute compile
Error: caused by: Compiler not supported: "error: Unrecognized option: \'E\'\n\n"
error: could not compile `rubyfmt-main`
Error: could not compile `rubyfmt-main`
To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
Warning: error: build failed
make: *** [Makefile:57: clippy] Error 101
Error: Process completed with exit code 2.

Searching for that error led me to this issue on clippy's bug tracker. This led me to believe upgrading the version of sccache installed in ci would help, since the version in use is two versions behind (2.13 vs 2.15). I got a different error message after upgrading.

Searching more led me to this issue on sccache's bug tracker which leads me to believe the latest rust release might have broken things.

[phiggins]

Updating to 0.2.15 does fix building on ubuntu-latest on CI. chmod +x on the sccache binary is what I was missing before.