Bump flexmark from 0.62.2 to 0.64.0 (#104)

Bumps [flexmark](https://github.com/vsch/flexmark-java) from 0.62.2 to 0.64.0.
- [Release notes](https://github.com/vsch/flexmark-java/releases)
- [Commits](vsch/flexmark-java@0.62.2...0.64.0)

---
updated-dependencies:
- dependency-name: com.vladsch.flexmark:flexmark
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]

spotify-web-api-java-generator/pom.xml

@@ -22,7 +22,7 @@
     <properties>
         <guava.version>31.1-jre</guava.version>
         <picocli.version>4.6.3</picocli.version>
-        <flexmark.version>0.62.2</flexmark.version>
+        <flexmark.version>0.64.0</flexmark.version>
         <mustache.java.version>0.9.10</mustache.java.version>
         <slf4j.version>1.7.36</slf4j.version>
         <swagger-parser.version>2.0.29</swagger-parser.version>