Minor comments fix in hbb_tutorials, chapters 6 & 7

[michalkornek]

In the file learn.py in hbb_tutorials, chapter 6, there are 2 errors/typos in the comments:

1. nengo-gui/nengo_gui/examples/hbb_tutorials/chapter6/learn.py

   Line 27 in 31428d6

   # communication channel in this case) and starts tracking the post population.

If I understand well, the comment in line 27 it should be:
"(...) and starts tracking the pre population."

2. nengo-gui/nengo_gui/examples/hbb_tutorials/chapter6/learn.py

   Line 82 in 31428d6

   #function to inhibit the error population after 25 seconds

Based on the code on lines 83-84 and on the observed simulation, the comment in line 82 it should be:
"(...) the error population after 15 seconds"

Not so sure about this one, but in all files in chapter 7, there is probably a typo in the comments in each of the examples, below is just a link to the first one:
3.

nengo-gui/nengo_gui/examples/hbb_tutorials/chapter7/1-spa_sequence.py

Line 65 in 31428d6

#Creating the BG and Thalamus components that confirm to the specified rules

I am not a native English speaker, but I believe it should be "conform" instead?

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