boost: add context dependency

libboost_coroutine needs libboost_context.  This should be resolved
automatically but we seem to not be doing so in some cases, so add
it manually.

Fixes openbmc/sdbusplus#46.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I1d3cb548f8c125eb49aaf1d21cab4740ddab6cfa
diff --git a/meson.build b/meson.build
index c45ea83..ec95c72 100644
--- a/meson.build
+++ b/meson.build
@@ -38,7 +38,7 @@
     'boost',
     disabler: true,
     required: false,
-    modules: [ 'coroutine' ],
+    modules: [ 'coroutine', 'context' ],
 )
 
 subdir('example')