Miscellaneous minor fixes

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,7 +5,7 @@ that is provided, the better.
 
 **Description of the changes being introduced by the pull request**:
 
-**Please verify and check that the pull request fulfills the following
+**Please verify and check that the pull request fulfils the following
 requirements**:
 
 - [ ] The code follows the [Code Style Guidelines](https://github.com/secure-systems-lab/code-style-guidelines#code-style-guidelines)

.travis.yml

@@ -10,6 +10,10 @@ matrix:
       env: TOXENV=py35
     - python: "3.6"
       env: TOXENV=py36
+    - python: "3.7"
+      env: TOXENV=py37
+    - python: "3.8"
+      env: TOXENV=py38
 
 install:
   - pip install -U tox coveralls

securesystemslib/exceptions.py

@@ -105,19 +105,6 @@ class UnsupportedLibraryError(Error):
   pass
 
 
-# TODO: Consider removal alongside the compression functions.
-class DecompressionError(Error):
-  """Indicate that some error happened while decompressing a file."""
-
-  def __init__(self, exception):
-    # Store the original exception.
-    self.exception = exception
-
-  def __str__(self):
-    # Show the original exception.
-    return repr(self.exception)
-
-
 class InvalidNameError(Error):
   """Indicate an error while trying to validate any type of named object."""
   pass

tests/test_interface.py

@@ -43,7 +43,6 @@
 else:
   import mock
 
-import securesystemslib.formats
 import securesystemslib.formats
 import securesystemslib.hash
 import securesystemslib.interface as interface

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py27, py35, py36
+envlist = py27, py35, py36, py37, py38
 skipsdist = True
 
 [testenv]