Update of Dockerfile

[Sinkmanu]

There is an error in Dockerfile because Github does not allow anymore the download of directories using svn (checkout or export). I wrote this in Issues because I do not know if PR are accepted.

Thus, change the following line:

RUN svn checkout https://github.com/llvm/llvm-project/tree/release/12.x/compiler-rt/lib/fuzzer

by:

RUN wget https://github.com/llvm/llvm-project/archive/refs/tags/llvmorg-12.0.0.tar.gz 
RUN tar --strip-components=3 -xvzf llvmorg-12.0.0.tar.gz llvm-project-llvmorg-12.0.0/compiler-rt/lib/fuzzer
RUN rm llvmorg-12.0.0.tar.gz