Unpin serde

[Mrmaxmeier]

This bumps the minimum required rustc version to 1.32.

Updating serde_derive breaks the builds for rustc < 1.32. See #203 for details.

$ cargo +stable -vV
cargo 1.31.0 (339d9f9c8 2018-11-16)
release: 1.31.0
commit-hash: 339d9f9c8f400010df3282ae5582bf3a0f739004
commit-date: 2018-11-16
$ cargo +stable build
[...]
$ ldd target/debug/cbindgen
	linux-vdso.so.1 (0x00007fff69b58000)
	libproc_macro-eb9b1f5dc4b73ebd.so => not found
	libsyntax-8b4b84ccec0d2e12.so => not found
	libsyntax_pos-31f39647344993a7.so => not found
	libstd-89cf9eb8d404bb7b.so => not found
	libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f0d4a1a8000)
	libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00007f0d4a18e000)
	libc.so.6 => /usr/lib/libc.so.6 (0x00007f0d49fc8000)
	/lib64/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007f0d4ac18000)
	libm.so.6 => /usr/lib/libm.so.6 (0x00007f0d49e43000)

After updating to today's stable release, this is no longer an issue. 🎉

$ cargo +stable -vV
cargo 1.32.0 (8610973aa 2019-01-02)
release: 1.32.0
commit-hash: 8610973aaf48615ba7dc9a38a9a2795ba6f36a31
commit-date: 2019-01-02
$ cargo +stable build
[...]
$ ldd target/debug/cbindgen
	linux-vdso.so.1 (0x00007ffed69b0000)
	libdl.so.2 => /usr/lib/libdl.so.2 (0x00007f9412875000)
	librt.so.1 => /usr/lib/librt.so.1 (0x00007f941286b000)
	libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f941284a000)
	libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00007f9412830000)
	libc.so.6 => /usr/lib/libc.so.6 (0x00007f941266c000)
	/lib64/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007f94132f7000)
	libm.so.6 => /usr/lib/libm.so.6 (0x00007f94124e7000)

Closes #203.

[eqrion]

I'm not sure we can do this yet because of Firefox's rust update policy. Firefox currently requires only 1.29, and cbindgen is used during the build.

But yes, I definitely want to do this ASAP.

cc @bholley @emilio

[bholley]

Yeah, from the stable+2weeks policy, we should be able to require 1.32 on Jan 31, which is a few days into the Firefox 67 Nightly cycle.

[konstin]

What's the status here? Having this PR released would really useful as it would finally allow publishing crates depending cbindgen and recent serde versions.

[eqrion]

I'll take a look at doing this now that we can require 1.32. Just got back from vacation.

[eqrion]

So it looks like Firefox doesn't yet require 1.32. I've posted a comment requesting that they increment the minimum required version.

[eqrion]

Looks like the patch to require 1.32 has been pushed. Once it's merged we should be able to do a release with this.