Symlink lua vapi to proper pkg-config package name

diff --git a/src/lua5.1.vapi b/src/lua5.1.vapi
new file mode 120000 (symlink)
index 0000000..e730dfc
--- /dev/null
+++ b/src/lua5.1.vapi
@@ -0,0 +1 @@
+/usr/share/vala/vapi/lua.vapi
\ No newline at end of file