[chore] Update Go version to 1.18 (#444)

* linting with new golangci-lint version

* update go to 1.18

* bump versions in drone.yml

* use new runtime/debug package for version info

* remove Commit build flag from goreleaser

* remove mock commit + version from build script

* go fmt

* add dummy version env flag to test container

* install git in golang container for testing

* only set versionString if Version is defined

scripts/build.sh

@@ -2,10 +2,7 @@
 
 set -eu
 
-COMMIT="${COMMIT:-1234567}"
-VERSION="${VERSION:-0.0.0}"
-
 CGO_ENABLED=0 go build -trimpath \
                        -tags 'netgo osusergo static_build' \
-                       -ldflags="-s -w -extldflags '-static' -X 'main.Commit=${COMMIT}' -X 'main.Version=${VERSION}'" \
+                       -ldflags="-s -w -extldflags '-static' -X 'main.Version=${VERSION:-$(git describe --tags --abbrev=0)}'" \
                        ./cmd/gotosocial