debug(ci): pin pnpm version;

- for Node 10

Author: lukeed

.github/workflows/ci.yml

@@ -17,12 +17,7 @@ jobs:
         node-version: ${{ matrix.nodejs }}
 
     - name: (env) pnpm
-      if: matrix.os == 'ubuntu-latest'
-      run: curl -f https://get.pnpm.io/v6.16.js | node - add --global pnpm
-
-    - name: (env) pnpm
-      if: matrix.os == 'windows-latest'
-      run: Invoke-WebRequest 'https://get.pnpm.io/v6.16.js' -UseBasicParsing -o pnpm.js; node pnpm.js add --global pnpm; Remove-Item pnpm.js
+      run: npm i -g pnpm@5.18
 
     - name: Install
       run: pnpm install