Remove library version from Composer install examples

By default, Composer installs the most recent stable version and declares a requirement with the caret operator (allowing any newer versions up to but not including the next major version).

Author: jmikola

source/tutorial/install-php-library.txt

@@ -33,7 +33,7 @@ root:
 
 .. code-block:: sh
 
-   composer require "mongodb/mongodb=^1.0.0"
+   composer require mongodb/mongodb
 
 While not recommended, you may also manually install the package via
 the source tarballs attached to the `GitHub releases