fix typo in Dockerfile

Dockerfile

@@ -16,7 +16,7 @@ RUN dpkg --add-architecture i386 && \
     apt-get install -y -q gcc git make net-tools libncurses5-dev \
     tftpd zlib1g-dev libssl-dev flex bison libselinux1 gnupg wget \
     diffstat chrpath socat xterm autoconf libtool tar unzip texinfo \
-    zlib1g-dev gcc-multilib build-essential -dev zlib1g:i386 screen pax gzip \
+    zlib1g-dev gcc-multilib build-essential zlib1g:i386 screen pax gzip \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/*