Clean up the Dockerfile (#405)

Avoid use of wget without progress bar.

Expressions don't expand in single quotes, use double quotes for that.

Author: jbampton

Dockerfile

@@ -21,7 +21,7 @@ RUN apk --no-cache add \
     git
 
 # Build and install LLVM
-RUN wget "https://github.com/llvm/llvm-project/archive/llvmorg-${LLVM_VERSION}.tar.gz" || { echo 'Error downloading LLVM version ${LLVM_VERSION}' ; exit 1; }
+RUN wget --progress=dot:giga "https://github.com/llvm/llvm-project/archive/llvmorg-${LLVM_VERSION}.tar.gz" || { echo "Error downloading LLVM version ${LLVM_VERSION}" ; exit 1; }
 
 RUN tar zxf llvmorg-${LLVM_VERSION}.tar.gz && rm llvmorg-${LLVM_VERSION}.tar.gz