pin pip to specific version to prevent errors

src/freedombone-app-matrix

@@ -758,7 +758,7 @@ function install_matrix {
             python-virtualenv sqlite unzip \
             zlib1g zlib1g-dev
 
-    pip install --upgrade pip
+    pip install --upgrade pip==9.0.3
     pip install --upgrade python-ldap
     pip install --upgrade lxml
     pip install --upgrade --force "phonenumbers>=8.2.0"

src/freedombone-utils-turn

@@ -177,7 +177,7 @@ function install_turn {
             python-virtualenv sqlite unzip \
             zlib1g zlib1g-dev
 
-    pip install --upgrade pip
+    pip install --upgrade pip==9.0.3
     pip install --upgrade python-ldap
     pip install --upgrade lxml