fix: update pnpm install flags

pnpm v7.0.0 until 7.13.5 uses `--strict-peer-dependencies=true` which causes
a failure when not all `peerDependencies` are installed. By setting the
flag explicitly, this will no longer be a problem for new users.

fix: #1806

lib/package-managers/pnpm.package-manager.ts

@@ -16,8 +16,8 @@ export class PnpmPackageManager extends AbstractPackageManager {
   // As of PNPM v5.3, all commands are shared with NPM v6.14.5. See: https://pnpm.js.org/en/pnpm-vs-npm
   get cli(): PackageManagerCommands {
     return {
-      install: 'install',
-      add: 'install',
+      install: 'install --strict-peer-dependencies=false',
+      add: 'install --strict-peer-dependencies=false',
       update: 'update',
       remove: 'uninstall',
       saveFlag: '--save',