Drop support for Go version 1.11

CONTRIBUTING.md

@@ -60,16 +60,11 @@ uploading it somewhere or post only the parts that are really relevant.
 Development Environment
 =======================
 
-The repository contains several sets of directories with code: `cmd/` and
-`internal/` contain the code written for restic, whereas `vendor/` contains
-copies of libraries restic depends on. The libraries are managed with the
-command `go mod vendor`.
+The repository contains the code written for restic in the directories
+`cmd/` and `internal/`.
 
-Go >= 1.11
-----------
-
-For Go version 1.11 or later, you should clone the repo (without having
-`$GOPATH` set) and `cd` into the directory:
+Restic requires Go version 1.12 or later for compiling. Clone the repo (without
+having `$GOPATH` set) and `cd` into the directory:
 
     $ unset GOPATH
     $ git clone https://github.com/restic/restic
@@ -79,40 +74,12 @@ Then use the `go` tool to build restic:
 
     $ go build ./cmd/restic
     $ ./restic version
-    restic 0.9.2-dev (compiled manually) compiled with go1.11 on linux/amd64
+    restic 0.9.6-dev (compiled manually) compiled with go1.14 on linux/amd64
 
 You can run all tests with the following command:
 
     $ go test ./...
 
-Go < 1.11
----------
-
-In order to compile restic with Go before 1.11, it needs to be checked out at
-the right path within a `GOPATH`. The concept of a `GOPATH` is explained in
-["How to write Go code"](https://golang.org/doc/code.html).
-
-If you do not have a directory with Go code yet, executing the following
-instructions in your shell will create one for you and check out the restic
-repo:
-
-    $ export GOPATH="$HOME/go"
-    $ mkdir -p "$GOPATH/src/github.com/restic"
-    $ cd "$GOPATH/src/github.com/restic"
-    $ git clone https://github.com/restic/restic
-    $ cd restic
-
-You can then build restic as follows:
-
-    $ go build ./cmd/restic
-    $ ./restic version
-    restic compiled manually
-    compiled with go1.8.3 on linux/amd64
-
-The following commands can be used to run all the tests:
-
-    $ go test ./...
-
 Providing Patches
 =================