Fix documentation inconsistency

Closes gh-2416

Author: snicoll

spring-boot/src/main/java/org/springframework/boot/context/embedded/ConfigurableEmbeddedServletContainer.java

@@ -56,7 +56,7 @@ public interface ConfigurableEmbeddedServletContainer {
 	void setSessionTimeout(int sessionTimeout);
 
 	/**
-	 * The session timeout in the specified {@link TimeUnit} (default 30 seconds). If 0 or
+	 * The session timeout in the specified {@link TimeUnit} (default 30 minutes). If 0 or
 	 * negative then sessions never expire.
 	 * @param sessionTimeout the session timeout
 	 * @param timeUnit the time unit