Fix npm run syntax tests (#928)

This changes the single quotes to double quotes in the syntax and grammar scripts.

Single quotes do not work on Windows, double quotes work everywhere and allow passing in arguments using `npm run test:snap -- -u`

package.json

@@ -336,8 +336,8 @@
     "test": "node ./out/test/runTest.js",
     "test:unit": "jest",
     "test:syntax": "npm run test:grammar && npm run test:snap",
-    "test:grammar": "npx vscode-tmgrammar-test -s source.terraform -g syntaxes/terraform.tmGrammar.json -t 'tests/unit/**/*.tf'",
-    "test:snap": "npx vscode-tmgrammar-snap -s source.terraform -g syntaxes/terraform.tmGrammar.json -t 'tests/snapshot/**/*.tf'",
+    "test:grammar": "npx vscode-tmgrammar-test -s source.terraform -g syntaxes/terraform.tmGrammar.json -t \"tests/unit/**/*.tf\"",
+    "test:snap": "npx vscode-tmgrammar-snap -s source.terraform -g syntaxes/terraform.tmGrammar.json -t \"tests/snapshot/**/*.tf\"",
     "lint": "eslint src --ext ts",
     "prettier": "prettier \"**/*.+(js|json|ts)\"",
     "format": "npm run prettier -- --write",