Upgrade to Mimepull 1.9.12

Closes gh-18790

Author: snicoll

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -134,7 +134,7 @@
 		<lombok.version>1.18.10</lombok.version>
 		<mariadb.version>2.3.0</mariadb.version>
 		<micrometer.version>1.1.7</micrometer.version>
-		<mimepull.version>1.9.11</mimepull.version>
+		<mimepull.version>1.9.12</mimepull.version>
 		<mockito.version>2.23.4</mockito.version>
 		<mongo-driver-reactivestreams.version>1.9.2</mongo-driver-reactivestreams.version>
 		<mongodb.version>3.8.2</mongodb.version>