Update to latest os for build and test

Signed-off-by: Derek McGowan <derek@mcg.dev>

.github/workflows/ci.yml

@@ -65,7 +65,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-18.04, macos-10.15]
+        os: [ubuntu-latest, macos-latest, windows-latest]
     name: ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     timeout-minutes: 5
@@ -84,11 +84,7 @@ jobs:
     - name: Test
       working-directory: src/github.com/containerd/ttrpc
       run: |
-        go test -v -race -coverprofile=coverage.txt -covermode=atomic ./...
-
-    - name: Codecov
-      run: bash <(curl -s https://codecov.io/bash)
-      working-directory: src/github.com/containerd/ttrpc
+        go test -v -race ./...
 
   #
   # Run Protobuild