sdevent: Support floating sources

This will be used by our source/base to support floating references.

Change-Id: I711d75b3552fe7f96f4c42e346741862999f1ee2
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/meson.build b/src/meson.build
index c41f6bf..fb47688 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -20,7 +20,7 @@
 endif
 
 sdeventplus_deps = [
-  dependency('libsystemd', version: '>=239'),
+  dependency('libsystemd', version: '>=240'),
   dependency('stdplus', fallback: ['stdplus', 'stdplus']),
   function2_dep,
 ]