update minimum versions of rc features

Author: steveklabnik

src/rust-2018/macros/macro-changes.md

@@ -1,6 +1,6 @@
 # Macro changes
 
-![Minimum Rust version: nightly](https://img.shields.io/badge/Minimum%20Rust%20Version-nightly-red.svg)
+![Minimum Rust version: beta](https://img.shields.io/badge/Minimum%20Rust%20Version-beta-orange.svg)
 
 In Rust 2018, you can import specific macros from external crates via `use`
 statements, rather than the old `#[macro_use]` attribute.

src/rust-2018/module-system/path-clarity.md

@@ -1,6 +1,6 @@
 # Path clarity
 
-![Minimum Rust version: nightly](https://img.shields.io/badge/Minimum%20Rust%20Version-nightly-red.svg)
+![Minimum Rust version: beta](https://img.shields.io/badge/Minimum%20Rust%20Version-beta-orange.svg)
 ![Minimum Rust version: nightly](https://img.shields.io/badge/Minimum%20Rust%20Version-nightly-red.svg) for "uniform paths"
 
 The module system is often one of the hardest things for people new to Rust. Everyone
@@ -224,7 +224,6 @@ and the submodule is still `foo/bar.rs`. This eliminates the special
 name, and if you have a bunch of files open in your editor, you can clearly
 see their names, instead of having a bunch of tabs named `mod.rs`.
 
-
 # Uniform paths
 
 > Uniform paths are a nightly-only feature.

src/rust-2018/module-system/raw-identifiers.md

@@ -1,6 +1,6 @@
 # Raw identifiers
 
-![Minimum Rust version: nightly](https://img.shields.io/badge/Minimum%20Rust%20Version-nightly-red.svg)
+![Minimum Rust version: beta](https://img.shields.io/badge/Minimum%20Rust%20Version-beta-orange.svg)
 
 Rust, like many programming languages, has the concept of "keywords".
 These identifiers mean something to the language, and so you cannot use them in

src/rust-2018/ownership-and-lifetimes/inference-in-structs.md

@@ -1,6 +1,6 @@
 # `T: 'a` inference in structs
 
-![Minimum Rust version: nightly](https://img.shields.io/badge/Minimum%20Rust%20Version-nightly-red.svg)
+![Minimum Rust version: beta](https://img.shields.io/badge/Minimum%20Rust%20Version-beta-orange.svg)
 
 An annotation in the form of `T: 'a`, where `T` is either a type or another
 lifetime, is called an *"outlives"* requirement. Note that *"outlives"* also

src/rust-2018/ownership-and-lifetimes/lifetime-elision-in-impl.md

@@ -1,6 +1,6 @@
 # Lifetime elision in impl
 
-![Minimum Rust version: nightly](https://img.shields.io/badge/Minimum%20Rust%20Version-nightly-red.svg)
+![Minimum Rust version: beta](https://img.shields.io/badge/Minimum%20Rust%20Version-beta-orange.svg)
 
 When writing `impl` blocks, you can now elide lifetime annotations in some
 situations.

src/rust-2018/ownership-and-lifetimes/the-anonymous-lifetime.md

@@ -100,4 +100,4 @@ impl Foo<'_, '_> {
 This is the same, because for each `'_`, a fresh lifetime is generated.
 Finally, the relationship `'a: 'b` which the struct requires must be upheld.
 
-For more details, see the [tracking issue on In-band lifetime bindings](https://github.com/rust-lang/rust/issues/44524).
+For more details, see the [tracking issue on In-band lifetime bindings](https://github.com/rust-lang/rust/issues/44524).

src/rust-2018/trait-system/no-anon-params.md

@@ -1,9 +1,12 @@
 # No more anonymous trait parameters
 
+![Minimum Rust version: beta](https://img.shields.io/badge/Minimum%20Rust%20Version-beta-orange.svg)
+
 In accordance with RFC [#1685](https://github.com/rust-lang/rfcs/pull/1685),
 parameters in trait method declarations are no longer allowed to be anonymous.
 
 For example, in the 2015 edition, this was allowed:
+
 ```rust
 trait Foo {
     fn foo(&self, u8);