Prevent two versions of pip

* docker-library/python#121 8726813

Author: JayH5

3.5/Dockerfile

@@ -31,7 +31,7 @@ RUN set -ex \
         && ./configure --enable-shared --enable-unicode=ucs4 \
         && make -j$(getconf _NPROCESSORS_ONLN) \
         && make install \
-      	&& pip3 install --no-cache-dir --upgrade --ignore-installed pip==$PYTHON_PIP_VERSION \
+        && pip3 install --no-cache-dir --upgrade pip==$PYTHON_PIP_VERSION \
       	&& find /usr/local -depth \
       		\( \
       		    \( -type d -a -name test -o -name tests \) \