Fix typo in dir, add dependencies to Dockerfile, cleanup

Author: telezhnaya

contact-builder/Dockerfile contract-builder/Dockerfile

@@ -5,4 +5,10 @@ LABEL description="Container for builds"
 RUN rustup default 1.51.0
 RUN rustup target add wasm32-unknown-unknown
 
-RUN apt-get update && apt-get install -y git less vim
+RUN apt-get update && apt-get install -y \
+    git \
+    less \
+    vim \
+    llvm \
+    clang \
+    && rm -rf /var/lib/apt/lists/*