fix compiling flags in dockerfile

Dockerfile

@@ -20,7 +20,7 @@ RUN git clone https://github.com/ggerganov/llama.cpp.git && \
         -DGGML_AVX2=ON \
         -DGGML_FMA=ON \
         -DGGML_F16C=OFF && \
-    cmake --build build --config Release --target llama-server -j$(nproc) && \
+    cmake --build build --config Release --target llama-server -j2 && \
     echo "=== Binary dependencies ===" && \
     ldd build/bin/llama-server || true