requirements: Relax Click version requirement

We were pinning the version of Click to 7.0.~. This was preventing
side-by-side installs with mbed-tools, as mbed-tools requires
Click>=7.1,<8.

Relax the Click version requirement to >7.0,<8 to prevent dependency
conflicts with mbed-tools.

Author: rwalton-arm

requirements.txt

@@ -27,5 +27,5 @@ pywin32==224;platform_system=='Windows'
 wmi==1.4.9;platform_system=='Windows'
 psutil==5.6.6
 cryptography>=2.5,<3
-Click>=7.0,<7.1
+Click>=7.0,<8
 cbor>=1.0.0