Update versions of syn/quote/proc-macro2

[bobtwinkles]

Setup

Add diesel = 1.3 to a crate's Cargo.toml

Versions

• Rust: rustc 1.29.0-nightly (12ed235ad 2018-07-18) or rustc 1.27.1 (5f2b325f6 2018-07-07)
• Diesel: 1.3.2
• Database: N/A
• Operating System N/A

Feature Flags

• diesel: N/A

Problem Description

Using serde and diesel in the same project result in 2 versions of the syn/quote/proc-macro2 constellation of crates being compiled. It would be better if this didn't happen.

What are you trying to accomplish?

Use serde and diesel in the same crate

What is the expected output?

Only one version of syn/quote/proc-macro2 is compiled.

What is the actual output?

Two versions are compiled:
From serde_derive 1.0.78 we have:

• proc-macro2 0.4.19
• quote 0.6.8
• syn 0.15.4

From diesel_derive 1.3.0:

• proc-macro2 0.3.8
• quote 0.5.2
• syn 0.13.11

Are you seeing any additional errors?

No.

Steps to reproduce

Add Serde and Diesel to the same crate

Checklist

• I have already looked over the issue tracker for similar issues.
• This issue can be reproduced on Rust's stable channel. (Your issue will be
  closed if this is not the case)

[bobtwinkles]

For what it's worth, I'm willing to take a stab at fixing this if nobody else is working on it.

[Eijebong]

54b21b0 It's already on master

[bobtwinkles]

Awesome, thanks!