fix(loader): look for themes on package.path

Author: mrcjkb

lua/lualine/utils/loader.lua

@@ -220,8 +220,12 @@ local function load_theme(theme_name)
   end
   local n_files = #files
   if n_files == 0 then
-    -- No match found
-    error(path .. ' Not found')
+    -- No match found on runtimepath. Fall back to package.path
+    local file = assert(
+      package.searchpath('lualine.themes.' .. theme_name, package.path),
+      'Theme ' .. theme_name .. ' not found'
+    )
+    retval = dofile(file)
   elseif n_files == 1 then
     -- when only one is found run that and return it's return value
     retval = dofile(files[1])