upgrade pip to fix wheel issues

Author: richarvey

Dockerfile

@@ -203,6 +203,7 @@ RUN echo @testing http://nl.alpinelinux.org/alpine/edge/testing >> /etc/apk/repo
     docker-php-ext-configure gd \
       --with-freetype \
       --with-jpeg
+RUN pip install --upgrade pip
     #curl iconv session
     #docker-php-ext-install pdo_mysql pdo_sqlite mysqli mcrypt gd exif intl xsl json soap dom zip opcache && \
     # docker-php-ext-install iconv pdo_mysql pdo_sqlite pgsql pdo_pgsql mysqli gd exif intl xsl json soap dom zip opcache && \