Add gtk2-devel package

Add gtk2-devel package requested by NOvA

worker/fnal-dev-sl7/Dockerfile

@@ -9,7 +9,8 @@ LABEL description="SL7 development container"
 RUN yum -y install asciidoc autoconf automake bzip2-devel fontconfig-devel freetype-devel ftgl-devel gdbm-devel giflib-devel gl2ps-devel glew-devel glibc-devel.i686 \
     harfbuzz-devel libAfterImage-devel libXft-devel libXi-devel libXrender-devel libgcc.i686 libjpeg-turbo-devel libpng-devel libstdc++-devel.i686 libtool \
     libuuid-devel libxkbcommon-devel libxkbcommon-x11-devel lz4-devel ncurses-devel openldap-devel perl-DBD-SQLite perl-ExtUtils-MakeMaker readline-devel \
-    subversion swig tcl-devel texinfo tk-devel xcb-util-image-devel xcb-util-keysyms-devel xcb-util-renderutil-devel xcb-util-wm-devel xmlto xxhash-devel zstd
+    subversion swig tcl-devel texinfo tk-devel xcb-util-image-devel xcb-util-keysyms-devel xcb-util-renderutil-devel xcb-util-wm-devel xmlto xxhash-devel zstd \
+    gtk2-devel
 
 RUN yum -y install python-six emacs vim \
     && yum -y clean all