Add clang-8, remove unused LLVM apt repos

clang-5.0 and clang-6.0 are provided by Ubuntu. Additionally, remove the
development branch repo because we do not install Clang from trunk.

Author: Lekensteyn

Dockerfile

@@ -2,9 +2,8 @@ FROM ubuntu:18.04
 ADD https://raw.githubusercontent.com/wireshark/wireshark/master/tools/debian-setup.sh /
 RUN apt update \
 	&& apt install gnupg apt-utils -y \
-	&& echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic main" > /etc/apt/sources.list.d/clang.list \
-	&& echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-6.0 main" > /etc/apt/sources.list.d/clang6.list \
 	&& echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-7 main" > /etc/apt/sources.list.d/clang7.list \
+	&& echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-8 main" > /etc/apt/sources.list.d/clang8.list \
 	&& apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6084F3CF814B57C1CF12EFD515CF4D18AF4F7421 \
 	&& apt update \
 	&& apt upgrade -y \
@@ -18,4 +17,5 @@ RUN apt update \
 		clang-5.0 \
 		clang-6.0 \
 		clang-7 \
+		clang-8 \
 	&& rm -rf /var/lib/apt/lists/