Use 'rm -rf' instead of 'rm -fr' (#1084)

Not super urgent, but seeing as it closes #927, might as well do now.

[skip changelog]

Makefile

@@ -60,4 +60,4 @@ endif
 tools:
 	git clone https://github.com/kennethreitz/pip-pop.git
 	mv pip-pop/bin/* vendor/pip-pop/
-	rm -fr pip-pop
+	rm -rf pip-pop

bin/compile

@@ -309,7 +309,7 @@ mtime "nltk.download.time" "${start}"
 # and copying it into the proper place (the logical place to do this was early, but it must be done here).
 # In CI, $BUILD_DIR is /app.
 if [[ ! "$BUILD_DIR" == "/app" ]]; then
-  rm -fr "$BUILD_DIR/.heroku/src"
+  rm -rf "$BUILD_DIR/.heroku/src"
   deep-cp /app/.heroku/src "$BUILD_DIR/.heroku/src"
 fi
 

bin/steps/pip-uninstall

@@ -16,7 +16,7 @@ if [ ! "$SKIP_PIP_INSTALL" ]; then
       mcount "failure.bad-requirements"
     fi
 
-    rm -fr requirements-declared.txt
+    rm -rf requirements-declared.txt
 
     if [[ -s .heroku/python/requirements-stale.txt ]]; then
       puts-step "Uninstalling stale dependencies"

bin/steps/python

@@ -84,13 +84,13 @@ mcount "version.python.${PYTHON_VERSION}"
 
 if [[ "$STACK" != "$CACHED_PYTHON_STACK" ]]; then
     puts-step "Stack has changed from $CACHED_PYTHON_STACK to $STACK, clearing cache"
-    rm -fr .heroku/python-stack .heroku/python-version .heroku/python .heroku/vendor .heroku/python .heroku/python-sqlite3-version
+    rm -rf .heroku/python-stack .heroku/python-version .heroku/python .heroku/vendor .heroku/python .heroku/python-sqlite3-version
 fi
 
 if [ -f .heroku/python-version ]; then
   if [ ! "$(cat .heroku/python-version)" = "$PYTHON_VERSION" ]; then
       puts-step "Found $(cat .heroku/python-version), removing"
-      rm -fr .heroku/python
+      rm -rf .heroku/python
   else
     SKIP_INSTALL=1
   fi

builds/libraries/sqlite

@@ -19,4 +19,4 @@ make install
 
 # Cleanup
 cd ..
-rm -fr sqlite
+rm -rf sqlite