Do not ignore AppVeyor failures on Node.js 12 (#77)

diff --git a/appveyor.yml b/appveyor.yml
index 1d4c45c..5267502 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -10,10 +10,6 @@
   - nodejs_version: 10
   - nodejs_version: 12
 
-matrix:
-  allow_failures:
-    - nodejs_version: 12
-
 install:
   - ps: Install-Product node $env:nodejs_version
   - npm install