Update pyqt5 requirement from <5.15,>=5.6 to >=5.6,<5.16

Updates the requirements on [pyqt5](https://www.riverbankcomputing.com/software/pyqt/) to permit the latest version.

Signed-off-by: dependabot-preview[bot] <[email protected]>

setup.py

@@ -58,7 +58,7 @@ def find_version(*file_paths):
         "Topic :: Communications :: File Sharing"
     ],
     install_requires=[
-        "pyqt5>=5.6, <5.15"
+        "pyqt5>=5.6, <5.16"
     ],
     python_requires='~=3.5'
 )