Dockerfile: Update runner base to alpine 3.10 (aquasecurity#199)

Signed-off-by: Manuel Rüger <[email protected]>

Dockerfile

@@ -8,7 +8,7 @@ COPY . /app/
 RUN go build -ldflags "-X main.version=$(git describe --tags --abbrev=0)" -a -o /trivy cmd/trivy/main.go
 RUN upx --lzma --best /trivy
 
-FROM alpine:3.9
+FROM alpine:3.10
 RUN apk --no-cache add ca-certificates git rpm
 COPY --from=builder /trivy /usr/local/bin/trivy