Update manifest tool to version 1.4.8 and install it from pypi

Author: arekzaluski

requirements.txt

@@ -19,7 +19,7 @@ mbed-greentea>=0.2.24,<1.7
 beautifulsoup4>=4,<=4.6.3
 fuzzywuzzy>=0.11,<=0.17
 pyelftools>=0.24,<=0.25
-git+https://github.com/armmbed/manifest-tool[email protected]
+manifest-tool==1.4.8
 icetea>=1.2.1,<1.3
 pycryptodome>=3.7.2,<=3.7.3
 pyusb>=1.0.0,<2.0.0