Added sdk to dockerignore

I've added the sdk directory to the docker ignore.
With the SDK ignored, we can install the SDK before
adding the project source. This allows the docker image
to preserve most of the layer caches when source code is
changed.

.dockerignore

@@ -1,3 +1,3 @@
 .dockerignore
 Dockerfile
-
+sdk

Dockerfile

@@ -10,16 +10,17 @@ RUN apt-get update && \
     pip install conan && \
     conan remote add bincrafters https://api.bintray.com/conan/bincrafters/public-conan
 
+# Install FBX SDK
+RUN mkdir -p /fbx2gltf/sdk/Linux/2019.2 && \
+    curl -L https://www.autodesk.com/content/dam/autodesk/www/adn/fbx/20192/fbx20192_fbxsdk_linux.tar.gz -o fbx20192_fbxsdk_linux.tar.gz && \
+    tar -xvf fbx20192_fbxsdk_linux.tar.gz && \
+    echo "yes\nn" | ./fbx20192_fbxsdk_linux /fbx2gltf/sdk/Linux/2019.2 && \
+    rm -rf /fbxsdktemp
+
 COPY . /fbx2gltf
 
 WORKDIR /fbx2gltf
 
-# Install FBX SDK
-RUN curl -L https://www.autodesk.com/content/dam/autodesk/www/adn/fbx/20192/fbx20192_fbxsdk_linux.tar.gz -o fbx20192_fbxsdk_linux.tar.gz && \
-	tar -xvf fbx20192_fbxsdk_linux.tar.gz && \
-	echo "yes\nn" | ./fbx20192_fbxsdk_linux /fbx2gltf/sdk/Linux/2019.2 && \
-	rm -rf /fbxsdktemp
-
 # Build and install
 RUN conan install . -i docker-build -s build_type=Release -s compiler=gcc -s compiler.version=5 -s compiler.libcxx=libstdc++11 && \
     conan build -bf docker-build . && \