Update Rust toolchain

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 8efe4b7..94ba1ed 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,7 +6,7 @@
 
 language: rust
 rust:
-  - nightly-2020-01-16
+  - nightly-2020-04-06
 
 os:
   - linux

rust-toolchain

diff --git a/rust-toolchain b/rust-toolchain
index 20d9cda..8bd4ff0 100644
--- a/rust-toolchain
+++ b/rust-toolchain
@@ -1 +1 @@
-nightly-2020-01-16
+nightly-2020-04-06