buildhistory_analysis: Convert stream data (bytes) to strings

The bytes type variables are threat different as strings variables in python3,
so convert bytes to strings. This was found when using the
script buildhistory-diff, where the interpreter was yielding this error

    TypeError: Type str doesn't support the buffer API

(From OE-Core rev: 3064d36186b47954eb94095217f7bb37e3fce651)

Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/buildhistory_analysis.py

@@ -190,7 +190,7 @@ class FileChange:
 
 
 def blob_to_dict(blob):
-    alines = blob.data_stream.read().splitlines()
+    alines = [line.decode() for line in blob.data_stream.read().splitlines()]
     adict = {}
     for line in alines:
         splitv = [i.strip() for i in line.split('=',1)]