configs: fix idmapped mounts json field names

In the runc state JSON we always use snake_case. This is a no-op change,
but it will cause any existing container state files to be incorrectly
parsed. Luckily, commit fbf183c ("Add uid and gid mappings to
mounts") has never been in a runc release so we can change this before a
1.2.z release.

Fixes: fbf183c ("Add uid and gid mappings to mounts")
Signed-off-by: Aleksa Sarai <[email protected]>

libcontainer/configs/mount_linux.go

@@ -34,13 +34,13 @@ type Mount struct {
 	// Note that, the underlying filesystem should support this feature to be
 	// used.
 	// Every mount point could have its own mapping.
-	UIDMappings []IDMap `json:"uidMappings,omitempty"`
+	UIDMappings []IDMap `json:"uid_mappings,omitempty"`
 
 	// GIDMappings is used to changing file group owners w/o calling chown.
 	// Note that, the underlying filesystem should support this feature to be
 	// used.
 	// Every mount point could have its own mapping.
-	GIDMappings []IDMap `json:"gidMappings,omitempty"`
+	GIDMappings []IDMap `json:"gid_mappings,omitempty"`
 }
 
 func (m *Mount) IsBind() bool {