deps: update dependency com.google.errorprone:error_prone_annotations to v2.4.0 (#172)

Co-authored-by: Elliotte Rusty Harold <elharo@users.noreply.github.com>
Co-authored-by: Jeff Ching <chingor@google.com>

Author: 3 people

build.gradle

@@ -44,7 +44,7 @@ ext {
       auto_value: 'com.google.auto.value:auto-value:1.7.4',
       guava: 'com.google.guava:guava:29.0-android',
       jsr305: 'com.google.code.findbugs:jsr305:3.0.2',
-      error_prone_annotations: 'com.google.errorprone:error_prone_annotations:2.3.4',
+      error_prone_annotations: 'com.google.errorprone:error_prone_annotations:2.4.0',
 
       // Testing
       junit: 'junit:junit:4.13.1',