[RESOLVED]HTTP error 500 : unable to include autoload.php

I'm facing problem on local versions of drupal that i've downloaded through git clone
However, I have two other drupal installations working perfectly(8.0.x via clone and 8.3.x-dev via .tar.gz)
git clone --branch 8.3.x https://git.drupal.org/project/drupal.git drupal83

I've cloned 8.3.x and 8.2.x using the above command and both of them return the same "HTTP ERROR 500".
On checking the apache log it says about some problems in including "autoload.php" as in the following lines

[Sun Dec 11 15:58:27.497148 2016] [:error] [pid 16120] [client 127.0.0.1:41224] PHP Warning:  require(/var/www/html/drupal82/vendor/autoload.php): failed to open stream: No such file or directory in /var/www/html/drupal82/autoload.php on line 14
[Sun Dec 11 15:58:27.497180 2016] [:error] [pid 16120] [client 127.0.0.1:41224] PHP Fatal error:  require(): Failed opening required '/var/www/html/drupal82/vendor/autoload.php' (include_path='.:/usr/share/php') in /var/www/html/drupal82/autoload.php on line 14
[Sun Dec 11 15:58:27.720691 2016] [:error] [pid 16271] [client 127.0.0.1:41226] PHP Warning:  require(/var/www/html/drupal82/vendor/autoload.php): failed to open stream: No such file or directory in /var/www/html/drupal82/autoload.php on line 14
[Sun Dec 11 15:58:27.720721 2016] [:error] [pid 16271] [client 127.0.0.1:41226] PHP Fatal error:  require(): Failed opening required '/var/www/html/drupal82/vendor/autoload.php' (include_path='.:/usr/share/php') in /var/www/html/drupal82/autoload.php on line 14

I've also edited apache config to AllowOverride

<Directory /var/www/>
	Options Indexes FollowSymLinks
	AllowOverride All
	Require all granted
</Directory>

and edited .htdocs to uncomment RewriteBase /