ci: remove AppVeyor (#415)

GitHub Actions can now do everything AppVeyor could for us, and more
(macOS support), and less jankily (_why_ can't go test invocations call
back into themselves, only on AppVeyor?).

Author: LawnGnome

.gitattributes

@@ -0,0 +1 @@
+* -text

.github/workflows/go-ci.yml

@@ -5,14 +5,17 @@ on:
 
 jobs:
   go-test:
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go-version: [1.14.x, 1.15.x]
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout
         uses: actions/checkout@v2
       - name: Set up Go
         uses: actions/setup-go@v2
         with:
-          go-version: 1.15
-      - run: go get -d -t ./...
+          go-version: ${{ matrix.go-version }}
       - run: go test -i ./...
       - run: go test -race -v ./...

DEVELOPMENT.md

@@ -38,11 +38,3 @@ For example, suppose we have the the recommended versions.
 If a new feature is added to a new `3.91.6` release of src-cli and this change requires only features available in Sourcegraph `3.99`, then this feature should also be present in a new `3.85.8` release of src-cli. Because a Sourcegraph instance will automatically select the highest patch version, all non-breaking changes should increment only the patch version. 
 
 Note that if instead the recommended src-cli version for Sourcegraph `3.99` was `3.90.4` in the example above, there is no additional step required, and the new patch version of src-cli will be available to both Sourcegraph versions.
-
-## AppVeyor builds
-
-We use AppVeyor to test `src-cli` on Windows.
-
-Configure the AppVeyor builds by editing the `appveyor.yml` file and logging in to AppVeyor and changing the settings there.
-
-Login with your GitHub account, switch to the `sourcegraph` account and change the settings here: https://ci.appveyor.com/project/sourcegraph/src-cli/settings/environment