Should allow only pdf files to be displayed when clicked on browse button.

[Rajat4Mahajan]

Since the logic is written for converting pdf to txt, streamlit uploader should not allow user to see other txt,docx,img etc files.

This can be achieved if we put type="pdf" in st.uploader

[costabm]

Thank you for your contribution @Rajat4Mahajan! I have added it to my pull request ( #45 )