removed global merge plugin installation

Author: schmunk42

php-7.1/Dockerfile-fpm

@@ -53,7 +53,6 @@ RUN npm install -g less lesshint google-closure-compiler
 
 ENV PHP_USER_ID=33 \
     PHP_ENABLE_XDEBUG=0 \
-    VERSION_COMPOSER_MERGE_PLUGIN=^1.3.1 \
     VERSION_COMPOSER_ASSET_PLUGIN=^1.2.0 \
     VERSION_PRESTISSIMO_PLUGIN=^0.3.0 \
     VERSION_CODECEPTION=^2.2.6 \
@@ -77,7 +76,6 @@ RUN curl -sS https://getcomposer.org/installer | php -- \
         --filename=composer.phar \
         --install-dir=/usr/local/bin && \
     composer global require --optimize-autoloader \
-        "wikimedia/composer-merge-plugin:${VERSION_COMPOSER_MERGE_PLUGIN}" \
         "fxp/composer-asset-plugin:${VERSION_COMPOSER_ASSET_PLUGIN}" \
         "hirak/prestissimo:${VERSION_PRESTISSIMO_PLUGIN}" && \
     composer global dumpautoload --optimize

php-7.1/Dockerfile-fpm-alpine

@@ -75,7 +75,6 @@ RUN npm install -g \
 # Configure version constraints
 ENV PHP_USER_ID=33 \
     PHP_ENABLE_XDEBUG=0 \
-    VERSION_COMPOSER_MERGE_PLUGIN=^1.3.1 \
     VERSION_COMPOSER_ASSET_PLUGIN=^1.2.2 \
     VERSION_PRESTISSIMO_PLUGIN=^0.3.0 \
     VERSION_CODECEPTION=^2.2.6 \
@@ -98,7 +97,6 @@ RUN curl -sS https://getcomposer.org/installer | php -- \
         --filename=composer.phar \
         --install-dir=/usr/local/bin && \
     composer global require --optimize-autoloader \
-        "wikimedia/composer-merge-plugin:${VERSION_COMPOSER_MERGE_PLUGIN}" \
         "fxp/composer-asset-plugin:${VERSION_COMPOSER_ASSET_PLUGIN}" \
         "hirak/prestissimo:${VERSION_PRESTISSIMO_PLUGIN}" && \
     composer global dumpautoload --optimize