[gobject-introspection] ci: Install Meson from PyPI

[Emmanuele Bassi <ebassi src gnome org>]

commit 400dcb3c496a47269688073e600395120a6a45c8
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Thu Mar 29 10:09:10 2018 +0100

    ci: Install Meson from PyPI
    
    The base Fedora image we use for CI doesn't always have the version of
    Meson we depend on; let's use Python's pip to install Meson, instead.

 .gitlab-ci/Dockerfile | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/.gitlab-ci/Dockerfile b/.gitlab-ci/Dockerfile
index 8ec66b00..01913f24 100644
--- a/.gitlab-ci/Dockerfile
+++ b/.gitlab-ci/Dockerfile
@@ -29,12 +29,18 @@ RUN dnf -y install \
     libxml2-devel \
     libxslt \
     mesa-libGL-devel \
-    meson \
+    ninja-build \
     pcre-devel \
+    python3 \
     python3-devel \
     python3-mako \
+    python3-pip \
+    python3-wheel \
     systemtap-sdt-devel \
-    zlib-devel
+    zlib-devel \
+ && dnf clean all
+
+RUN pip3 install meson
 
 ARG HOST_USER_ID=5555
 ENV HOST_USER_ID ${HOST_USER_ID}
@@ -43,4 +49,4 @@ RUN useradd -u $HOST_USER_ID -ms /bin/bash user
 USER user
 WORKDIR /home/user
 
-ENV LANG C.utf8
+ENV LANG C.UTF-8