Update Javadoc task to not use module directories. (#1290)

Author: dcr-stripe

build.gradle

@@ -122,6 +122,17 @@ coveralls {
     jacocoReportPath "build/reports/jacoco/test/jacocoTestReport.xml"
 }
 
+javadoc {
+  doFirst {
+    // We should remove this once we start using module-info.java.
+    // Without that file, Javadoc will fall back to "undefined" as the module
+    // name resulting in broken search links. This option explicitly declares
+    // that we are not currently using modules and the module name should be
+    // omitted from Javadoc.
+    options.addBooleanOption('-no-module-directories', true)
+  }
+}
+
 gitPublish {
     repoUri = '[email protected]:stripe/stripe-java.git'
     branch = 'gh-pages'