fix($core): theme/styles/palette.styl doesn't work

BTW, remove Object usage of palette.

packages/@vuepress/core/lib/build.js

@@ -26,7 +26,7 @@ module.exports = async function build (sourceDir, cliOptions = {}) {
     return console.error(logger.error(chalk.red('Unexpected option: outDir cannot be set to the current working directory.\n'), false))
   }
   await fs.remove(outDir)
-  logger.debug('Dist directory: ' + chalk.gray(require('path').resolve(process.cwd(), outDir)))
+  logger.debug('Dist directory: ' + chalk.gray(path.resolve(process.cwd(), outDir)))
 
   let clientConfig = createClientConfig(options, cliOptions).toConfig()
   let serverConfig = createServerConfig(options, cliOptions).toConfig()

packages/@vuepress/core/lib/internal-plugins/palette/index.js

@@ -24,23 +24,21 @@ module.exports = (options, ctx) => ({
     // 2. write palette.styl
     const { sourceDir, writeTemp } = ctx
 
-    const themePalette = ctx.themePalette
-    const { palette: userPalette } = ctx.siteConfig
-    const palettePath = path.resolve(sourceDir, '.vuepress/styles/palette.styl')
+    const themePalette = path.resolve(ctx.themePath, 'styles/palette.styl')
+    const userPalette = path.resolve(sourceDir, '.vuepress/styles/palette.styl')
 
     const themePaletteContent = resolvePaletteContent(themePalette)
     const userPaletteContent = resolvePaletteContent(userPalette)
-    const userPaletteContent2 = resolvePaletteContent(palettePath)
 
     // user's palette can override theme's palette.
-    const paletteContent = themePaletteContent + userPaletteContent + userPaletteContent2
+    const paletteContent = themePaletteContent + userPaletteContent
     await writeTemp('palette.styl', paletteContent)
   }
 })
 
 /**
  * resolve palette content
- * @param {string|object} palette
+ * @param {string} palette
  * @returns {string}
  */
 
@@ -55,14 +53,8 @@ function resolvePaletteContent (palette) {
     return ''
   }
 
-  if (isString(palette)) {
-    if (fs.existsSync(palette)) {
-      return `@import(${JSON.stringify(palette)})\n`
-    }
-    return ''
-  } else if (isPlainObject(palette)) {
-    return Object.keys(palette).map(variableName => {
-      return `${variableName} = ${palette[variableName]}`
-    }).join('\n') + '\n'
+  if (isString(palette) && fs.existsSync(palette)) {
+    return `@import(${JSON.stringify(palette)})\n`
   }
+  return ''
 }

packages/@vuepress/core/lib/prepare/loadTheme.js

@@ -69,8 +69,6 @@ module.exports = async function loadTheme (ctx) {
   }
 
   // handle theme api
-  const { palette: themePalette } = themeEntryFile
-
   const layoutDirs = [
     path.resolve(themePath, 'layouts'),
     path.resolve(themePath, '.')
@@ -135,7 +133,6 @@ module.exports = async function loadTheme (ctx) {
     themePath,
     layoutComponentMap,
     themeEntryFile,
-    themePalette,
     themeName,
     themeShortcut
   }