ci: add node 14 to workflow (#157)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d38ad9a..b4c04cf 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,7 +27,7 @@
 
     strategy:
       matrix:
-        node-version: [10.x, 12.x]
+        node-version: [10.x, 12.x, 14.x]
         os: [ubuntu-latest, windows-latest, macos-latest]
 
     steps: