Update sirbrillig/phpcs-variable-analysis requirement (#124)

Updates the requirements on [sirbrillig/phpcs-variable-analysis](https://github.com/sirbrillig/phpcs-variable-analysis) to permit the latest version.
- [Release notes](https://github.com/sirbrillig/phpcs-variable-analysis/releases)
- [Commits](sirbrillig/phpcs-variable-analysis@v2.10.2...v2.11.0)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

composer.json

@@ -11,7 +11,7 @@
   "require": {
     "php": "^7.1",
     "phpcompatibility/phpcompatibility-wp": "2.1.1",
-    "sirbrillig/phpcs-variable-analysis": "2.10.2",
+    "sirbrillig/phpcs-variable-analysis": "2.11.0",
     "slevomat/coding-standard": "6.4.1",
     "wp-coding-standards/wpcs": "2.3.0"
   },