Php-amqplib: php ext-bcmath required

[helloEson]

The production environment hosts may does not have bc-mach extension installed.
Could you please update this requirement to Readme.md file?

`# composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.

Problem 1
- php-amqplib/php-amqplib v2.6.3 requires ext-bcmath * -> the requested PHP extension bcmath is missing from your system.
- php-amqplib/php-amqplib v2.6.3 requires ext-bcmath * -> the requested PHP extension bcmath is missing from your system.
- Installation request for php-amqplib/php-amqplib v2.6.3 -> satisfiable by php-amqplib/php-amqplib[v2.6.3].
`

[mente]

AFAIK this is needed only for php7

[bouke-nederstigt]

Actually just ran into this problem as well.
The php 5.6 version from https://launchpad.net/~ondrej/+archive/ubuntu/php does not include the bcmath and mbstring extensions by default. Without them it's not possible to run composer.

[nubeiro]

Readme is already updated in master branch.