updated requirements.txt filename in docker

Business_cards/Dockerfile

@@ -8,7 +8,7 @@ WORKDIR /opt/bussinesscards
 COPY . .
 
 # Install any needed packages specified in requirements.txt
-RUN pip install --no-cache-dir -r requirement.txt
+RUN pip install --no-cache-dir -r mainrequirements.txt
 
 # Make port 80 available to the world outside this container
 EXPOSE 1112