use yarn in extension scripts

extensions/css/package.json

@@ -16,8 +16,7 @@
   "scripts": {
     "compile": "gulp compile-extension:css-client && gulp compile-extension:css-server",
     "postinstall": "cd server && yarn install",
-    "install-client-next": "npm install vscode-languageclient@next -f -S",
-    "install-client-local": "npm install ../../../vscode-languageserver-node/client -f -S",
+    "install-client-next": "yarn add vscode-languageclient@next",
     "update-grammar": "node ../../build/npm/update-grammar.js atom/language-css grammars/css.cson ./syntaxes/css.tmLanguage.json"
   },
   "contributes": {
@@ -720,4 +719,4 @@
   "devDependencies": {
     "@types/node": "7.0.43"
   }
-}
+}
\ No newline at end of file

extensions/html/package.json

@@ -17,8 +17,7 @@
     "compile": "gulp compile-extension:html-client && gulp compile-extension:html-server",
     "postinstall": "cd server && yarn install",
     "update-grammar": "node ../../build/npm/update-grammar.js textmate/html.tmbundle Syntaxes/HTML.plist ./syntaxes/html.json",
-    "install-client-next": "npm install vscode-languageclient@next -f -S",
-    "install-client-local": "npm install ../../../vscode-languageserver-node/client -f -S"
+    "install-client-next": "yarn add vscode-languageclient@next"
   },
   "contributes": {
     "languages": [

extensions/json/package.json

@@ -14,8 +14,7 @@
   "scripts": {
     "compile": "gulp compile-extension:json-client && gulp compile-extension:json-server",
     "postinstall": "cd server && yarn install",
-    "install-client-next": "npm install vscode-languageclient@next -f -S",
-    "install-client-local": "npm install ../../../vscode-languageserver-node/client -f -S",
+    "install-client-next": "yarn add vscode-languageclient@next",
     "update-grammar": "node ../../build/npm/update-grammar.js Microsoft/vscode-JSON.tmLanguage JSON.tmLanguage ./syntaxes/JSON.tmLanguage.json"
   },
   "contributes": {