appveyor.yml: use one type of indentation

2 spaces as in `travis.yml` and in the beginning of this file:

```
platform:
  - x86
  - x64
```

To make this united.

appveyor.yml

@@ -6,30 +6,30 @@ platform:
 clone_folder: c:\projects\composer
 
 cache:
-    - c:\tools\php -> appveyor.yml
+  - c:\tools\php -> appveyor.yml
 
 init:
-    - SET PATH=C:\Program Files\OpenSSL;c:\tools\php;%PATH%
-    - SET COMPOSER_NO_INTERACTION=1
-    - SET PHP=1
-    - SET ANSICON=121x90 (121x90)
+  - SET PATH=C:\Program Files\OpenSSL;c:\tools\php;%PATH%
+  - SET COMPOSER_NO_INTERACTION=1
+  - SET PHP=1
+  - SET ANSICON=121x90 (121x90)
 
 install:
-    - IF EXIST c:\tools\php (SET PHP=0)
-    - IF %PHP%==1 cinst -y OpenSSL.Light
-    - IF %PHP%==1 cinst -y php
-    - cd c:\tools\php
-    - IF %PHP%==1 copy php.ini-production php.ini /Y
-    - IF %PHP%==1 echo date.timezone="UTC" >> php.ini
-    - IF %PHP%==1 echo extension_dir=ext >> php.ini
-    - IF %PHP%==1 echo extension=php_openssl.dll >> php.ini
-    - IF %PHP%==1 echo extension=php_mbstring.dll >> php.ini
-    - IF %PHP%==1 echo extension=php_fileinfo.dll >> php.ini
-    - IF %PHP%==1 echo @php %%~dp0composer.phar %%* > composer.bat
-    - appveyor DownloadFile https://getcomposer.org/composer.phar
-    - cd c:\projects\composer
-    - composer install --prefer-dist --no-progress
+  - IF EXIST c:\tools\php (SET PHP=0)
+  - IF %PHP%==1 cinst -y OpenSSL.Light
+  - IF %PHP%==1 cinst -y php
+  - cd c:\tools\php
+  - IF %PHP%==1 copy php.ini-production php.ini /Y
+  - IF %PHP%==1 echo date.timezone="UTC" >> php.ini
+  - IF %PHP%==1 echo extension_dir=ext >> php.ini
+  - IF %PHP%==1 echo extension=php_openssl.dll >> php.ini
+  - IF %PHP%==1 echo extension=php_mbstring.dll >> php.ini
+  - IF %PHP%==1 echo extension=php_fileinfo.dll >> php.ini
+  - IF %PHP%==1 echo @php %%~dp0composer.phar %%* > composer.bat
+  - appveyor DownloadFile https://getcomposer.org/composer.phar
+  - cd c:\projects\composer
+  - composer install --prefer-dist --no-progress
 
 test_script:
-    - cd c:\projects\composer
-    - vendor/bin/phpunit --colors=always
+  - cd c:\projects\composer
+  - vendor/bin/phpunit --colors=always