[Tests] add node 15 to appveyor, fix "latest npm" logic

Author: ljharb

appveyor.yml

@@ -4,6 +4,9 @@ build: off
 
 environment:
   matrix:
+    - nodejs_version: "15"
+    - nodejs_version: "14"
+    - nodejs_version: "13"
     - nodejs_version: "12"
     - nodejs_version: "11"
     - nodejs_version: "10"
@@ -25,6 +28,7 @@ matrix:
   allow_failures:
     - nodejs_version: "5" # due to windows npm bug, registry-side
     - nodejs_version: "0.8"
+      # platform: x86 # x64 has started failing on the registry side, around early November 2020
     - nodejs_version: "0.6"
 
 platform:
@@ -33,17 +37,33 @@ platform:
 
 # Install scripts. (runs after repo cloning)
 install:
- # Fix symlinks in working copy (see https://github.com/appveyor/ci/issues/650#issuecomment-186592582) / https://github.com/charleskorn/batect/commit/d08986802ec43086902958c4ee7e57ff3e71dbef
- - git config core.symlinks true
- - git reset --hard
- # Get the latest stable version of Node.js or io.js
- - ps: Install-Product node $env:nodejs_version $env:platform
- - IF %nodejs_version% EQU 0.6 npm config set strict-ssl false && npm -g install npm@1.3
- - IF %nodejs_version% EQU 0.8 npm config set strict-ssl false && npm -g install npm@1.4.28 && npm install -g npm@4.5
- - set PATH=%APPDATA%\npm;%PATH%
- #- IF %nodejs_version% NEQ 0.6 AND %nodejs_version% NEQ 0.8 npm -g install npm
- # install modules
- - npm install
+  # Fix symlinks in working copy (see https://github.com/appveyor/ci/issues/650#issuecomment-186592582) / https://github.com/charleskorn/batect/commit/d08986802ec43086902958c4ee7e57ff3e71dbef
+  - git config core.symlinks true
+  - git reset --hard
+  # Get the latest stable version of Node.js or io.js
+  - ps: if ($env:nodejs_version -ne '0.6') { Install-Product node $env:nodejs_version $env:platform }
+  - ps: Update-NodeJsInstallation (Get-NodeJsLatestBuild $env:nodejs_version) $env:platform
+  - IF %nodejs_version% EQU 0.6 npm config set strict-ssl false && npm -g install npm@1.3
+  - IF %nodejs_version% EQU 0.8 npm config set strict-ssl false && npm -g install npm@1.4.28 && npm install -g npm@4.5
+  - IF %nodejs_version% EQU 1 npm -g install npm@2.9
+  - IF %nodejs_version% EQU 2 npm -g install npm@4
+  - IF %nodejs_version% EQU 3 npm -g install npm@4
+  - IF %nodejs_version% EQU 4 npm -g install npm@5.3
+  - IF %nodejs_version% EQU 5 npm -g install npm@5.3
+  - IF %nodejs_version% EQU 6 npm -g install npm@6.9
+  - IF %nodejs_version% EQU 7 npm -g install npm@6
+  - IF %nodejs_version% EQU 8 npm -g install npm@6
+  - IF %nodejs_version% EQU 9 npm -g install npm@6.9
+  - IF %nodejs_version% EQU 10 npm -g install npm@7
+  - IF %nodejs_version% EQU 11 npm -g install npm@7
+  - IF %nodejs_version% EQU 12 npm -g install npm@7
+  - IF %nodejs_version% EQU 13 npm -g install npm@7
+  - IF %nodejs_version% EQU 14 npm -g install npm@7
+  - IF %nodejs_version% EQU 15 npm -g install npm@7
+  - set PATH=%APPDATA%\npm;%PATH%
+  #- IF %nodejs_version% NEQ 0.6 AND %nodejs_version% NEQ 0.8 npm -g install npm
+  # install modules
+  - npm install
 
 # Post-install test scripts.
 test_script: