pthread currently does not support 7.1-zts

[vkijensky]

The latest pthread commit compatible with 7.1-zts is "70040812d22798c3dd4cfc3b612bd9f56a1dc7ba"
Description: amphp/parallel#10

Suggestion:
Remove pthread support, update project to 7.2-zts (still beta) or downgrade pthread.

You can deploy and build the pthread commit if you extend build command after is cloned e.g.:
&& git reset --hard 70040812d22798c3dd4cfc3b612bd9f56a1dc7ba

docker-php/7.1/zts/Dockerfile

Line 41 in 9aa9579

RUN git clone https://github.com/krakjoe/pthreads.git \