Update appveyor.yml

Author: aidanharan

appveyor.yml

@@ -36,6 +36,7 @@ environment:
   matrix:
     - ruby_version: "25-x64"
     - ruby_version: "26-x64"
+  matrix:
     allow_failures:
       - ruby_version: "25"     # Fails because of "File does not exist: tiny_tds/tiny_tds" error (See https://github.com/rails-sqlserver/tiny_tds/issues/391).
       - ruby_version: "26"     # Fails because of "File does not exist: tiny_tds/tiny_tds" error (See https://github.com/rails-sqlserver/tiny_tds/issues/391).