Merge pull request #306 from rust-lang/nrc-patch-1

Update 2018-12-06-Rust-1.31-and-rust-2018.md

Author: steveklabnik

posts/2018-12-06-Rust-1.31-and-rust-2018.md

@@ -350,6 +350,9 @@ Work on IDE support is not finished, in particular code completion is not up
 to scratch in the RLS-based editors. However, if you mainly want support for
 types, documentation, and 'go to def', etc. then you should be happy.
 
+If you have problems installing any of the tools with Rustup, try running
+`rustup self update`, and then try again.
+
 ### Tool lints
 
 In [Rust 1.30](https://blog.rust-lang.org/2018/10/25/Rust-1.30.0.html), we