Bump minimum version to 1.18

Author: sfackler

README.md

@@ -50,7 +50,7 @@ fn main() {
 ```
 
 ## Requirements
-* **Rust** - Rust-Postgres is developed against the 1.16 release of Rust
+* **Rust** - Rust-Postgres is developed against the 1.18 release of Rust
     available on http://www.rust-lang.org. It should also compile against more
     recent releases.
 

circle.yml

@@ -3,7 +3,7 @@ jobs:
   build:
     working_directory: ~/build
     docker:
-      - image: jimmycuadra/rust:1.17.0
+      - image: jimmycuadra/rust:1.18.0
       - image: sfackler/rust-postgres-test:1
     steps:
       - checkout