description.md: rm trailing spaces

One might assume that we can consider a CI check that there are no
trailing spaces, but we have to be careful because some embedded strings
that serve as example outputs are expected to have trailing spaces. The
currently only example is ocr-numbers. One might consider a CI check,
but simply exclude that file.

exercism/problem-specifications#995

Author: petertseng

exercises/nucleotide-count/README.md

@@ -2,8 +2,8 @@
 
 Given a single stranded DNA string, compute how many times each nucleotide occurs in the string.
 
-The genetic language of every living thing on the planet is DNA. 
-DNA is a large molecule that is built from an extremely long sequence of individual elements called nucleotides. 
+The genetic language of every living thing on the planet is DNA.
+DNA is a large molecule that is built from an extremely long sequence of individual elements called nucleotides.
 4 types exist in DNA and these differ only slightly and can be represented as the following symbols: 'A' for adenine, 'C' for cytosine, 'G' for guanine, and 'T' thymine.
 
 Here is an analogy:

exercises/rectangles/README.md

@@ -37,27 +37,27 @@ The above diagram contains 6 rectangles:
 ```
 
 ```text
-       
-       
+
+
    +--+
    |  |
    +--+
 ```
 
 ```text
-       
-       
+
+
 +--+
 |  |
 +--+
 ```
 
 ```text
-       
-  ++   
-  ++   
-       
-       
+
+  ++
+  ++
+
+
 ```
 
 You may assume that the input is always a proper rectangle (i.e. the length of