feat(cli): support build watch mode

packages/vant-cli/yarn.lock

@@ -2942,6 +2942,21 @@ chokidar@^2.0.2, chokidar@^2.1.8:
   optionalDependencies:
     fsevents "^1.2.7"
 
+chokidar@^3.3.1:
+  version "3.3.1"
+  resolved "http://registry.npm.qima-inc.com/chokidar/download/chokidar-3.3.1.tgz#c84e5b3d18d9a4d77558fef466b1bf16bbeb3450"
+  integrity sha1-yE5bPRjZpNd1WP70ZrG/FrvrNFA=
+  dependencies:
+    anymatch "~3.1.1"
+    braces "~3.0.2"
+    glob-parent "~5.1.0"
+    is-binary-path "~2.1.0"
+    is-glob "~4.0.1"
+    normalize-path "~3.0.0"
+    readdirp "~3.3.0"
+  optionalDependencies:
+    fsevents "~2.1.2"
+
 chownr@^1.1.1:
   version "1.1.3"
   resolved "https://registry.npm.taobao.org/chownr/download/chownr-1.1.3.tgz?cache=0&sync_timestamp=1569418652330&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2Fchownr%2Fdownload%2Fchownr-1.1.3.tgz#42d837d5239688d55f303003a508230fa6727142"
@@ -4886,7 +4901,7 @@ fsevents@^1.2.7:
     nan "^2.12.1"
     node-pre-gyp "^0.12.0"
 
-fsevents@~2.1.1:
+fsevents@~2.1.1, fsevents@~2.1.2:
   version "2.1.2"
   resolved "https://registry.npm.taobao.org/fsevents/download/fsevents-2.1.2.tgz?cache=0&sync_timestamp=1573319284429&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2Ffsevents%2Fdownload%2Ffsevents-2.1.2.tgz#4c0a1fb34bc68e543b4b82a9ec392bfbda840805"
   integrity sha1-TAofs0vGjlQ7S4Kp7Dkr+9qECAU=
@@ -8263,7 +8278,7 @@ performance-now@^2.1.0:
   resolved "https://registry.npm.taobao.org/performance-now/download/performance-now-2.1.0.tgz#6309f4e0e5fa913ec1c69307ae364b4b377c9e7b"
   integrity sha1-Ywn04OX6kT7BxpMHrjZLSzd8nns=
 
-picomatch@^2.0.4, picomatch@^2.0.5:
+picomatch@^2.0.4, picomatch@^2.0.5, picomatch@^2.0.7:
   version "2.1.1"
   resolved "https://registry.npm.taobao.org/picomatch/download/picomatch-2.1.1.tgz#ecdfbea7704adb5fe6fb47f9866c4c0e15e905c5"
   integrity sha1-7N++p3BK21/m+0f5hmxMDhXpBcU=
@@ -8927,6 +8942,13 @@ readdirp@~3.2.0:
   dependencies:
     picomatch "^2.0.4"
 
+readdirp@~3.3.0:
+  version "3.3.0"
+  resolved "http://registry.npm.qima-inc.com/readdirp/download/readdirp-3.3.0.tgz#984458d13a1e42e2e9f5841b129e162f369aff17"
+  integrity sha1-mERY0ToeQuLp9YQbEp4WLzaa/xc=
+  dependencies:
+    picomatch "^2.0.7"
+
 realpath-native@^1.1.0:
   version "1.1.0"
   resolved "https://registry.npm.taobao.org/realpath-native/download/realpath-native-1.1.0.tgz#2003294fea23fb0672f2476ebe22fcf498a2d65c"